Editor's Note: This growing directory is manually maintained and automatically tested for broken links once a month. Links which appear broken for three or more consecutive months are deleted.

Should there be anything wrong with an entry, let me know and I will be glad to correct it.
Note: an entry can appear in several categories.

INSTITUTIONS, Associations and Groups

• International:
• BIPM, Bureau des Poids et Mesures. Home page of the SI System of Units ... and much more
• CODATA, Committee on Data for Science and Technology.
• IAU, International Astronomical Union.
• ICTP, International Centre for Theoretical Physics. Located in Trieste (Italy).
• International Space Station, up there in the orbit. Website maintained by NASA.
• ISIS, the World centre for science with neutrons & muons.
• LHC, the Large Hadron Collider at CERN.
• Light Sources, a worldwide directory of accelerator-based sources of EM waves.
• SPIE, the International Society for Optical Engineering
• Europe:
• IOP, Institute of Physics UK, but now international.
• ASI, Agenzia Spaziale Italiana
• CERN, the largest European physics research center
• DESY, Deutsches Elektronen-Synchrotrone
• ESA, European Space Agency
• ESO, European Southern Observatory
• GSI, Gesselschaft für Schwerionenforschung, Germany
• INAF, Istituto Nazionale di Astrofisica, Italy
• INFN, Istituto Nazionale di Fisica Nucleare, Italy
     They run also the LNGS, the National Laboratories of Gran Sasso
• National Physical Laboratory, UK
• Nucleonica, an official EU nuclear-science website. They maintain the Karlsruhe Nuclide Chart
• Bourbaphy, Séminaire Poincaré, France
• SIF, Società Italiana di Fisica
• The Virtual Telescope. A privately funded Italian project
• USA:
• AAPT, American Association of Physics Teachers
• AIP, American Institute of Physics
• ANL, Argonne National Laboratory. A US Department of Energy laboratory
• APS, American Physics Society. Now international. I am a member and it is worth it!
• BNL, Brookhaven National Laboratory
• FermiLab, Fermi National Accelerator Laboratory, Batavia Ill.
• Johns Hopkins Applied Physics Laboratory
• JPL, Jet Propulsion Laboratory
• KITP. Kavli Institute of Theoretical Physics at University of California, Santa Barbara
• LANL, Los Alamos National Laboratory
• LBL, Berkeley National Laboratory
• LLNL, Lawrence Livermore National Laboratory
• MIT, Massachusetts Institute of Technology
• NASA, National Space Agency
• NHMFL, National High Magnetic Field Laboratory at Tallahassee, Florida.
• NIST Physics at National Institute of Standards.
• NNDC. National Nuclear Data Center.
• NRAO, National Radio Astronomy Laboratory.
• NSLS, National Synchrotron Light Source at Brookhaven
• NUFORC, the National UFO Reporting Center
• SLAC, National Accelerator Laboratory (Stanford Linear Accelerator)
• Elsewhere:
• AIST, National Institute of Advanced Industrial Science and Technology, Japan
• IHEP, Institute of High Energy Physics
  of the Russion Federation Governmental Scientific Center, Russia
• Landau Institute for Theoretical Physics in Moscow, Russia.
• Laval University Physics Department, Canada

JOURNALS and Magazines

• Open Access Physics Journals. Last count: 1550
• APS journals, a selection:
•    Physical Review Letters
•    Reviews of Modern Physics
•    Physical Review X, Free, open access
• AIP journals, a selection:
•    Journal of Chemical Physics
• European Journal of Physics
• Riviste della Società Italiana di Fisica
• Wiley Physics website with a complete list of Wiley-Blackwell physics Journals.
• The Abraham Zelmanov Journal for general relativity, gravitation and cosmology. Archive only
• Online e-Zines, Magazines, Forums:
• Physics of APS.
• Physics Today of AIP.
• Physics World of IOP.
• Fermilab Today
• MIT Technology Review
• Physics Classroom magazine
• FQXi, a speculative Physics forum on Foundational Questions Institute
• The Industrial Physicist historic archive (up to 2005). AIP.
• Sci.Physics Google group
• Physics Forums, a list reaching to other sciences as well. Overrun by trolls?
• Blogs:
• Azimuth of John Carlos Baez. This is not about Physics, it is Math and ++, too. But it is good :-)
• Nucleonica blog.
• Physics and Physicists, ZapperZ's blog.
• Theoretical physics blog of Matt Strassler.
• In the dark blog of Pete Coles.

ENCYCLOPEDIAs and Dictionaries and Wikis

• Astronomy Thesaurus by the Shobbrooks.
• Encyclopeadia Britannica.
• Magnetismus A-Z, amazing and well done hypertext dictionary of magnetics - in German.
• Microsoft Encarta Dictionary.
• Microsoft Encarta Encyclopedia.
• The Worlds of David Darling. Astronomy, Space, Alternative energy, Sustainable living.
• Units of Measurements Dictionary by Russ Rowlett at UNC.
• Weisstein's Dictionaries (by Eric Weisstein).
• Physics Wikis and similar resources:
• Wikipedia Free Web encyclopedia.
• Nucleonica Wiki.
• PaRMa Wiki managed by Roberto DeRenzi.

DATABASES and Directories

• arXive, huge repository of free scientific articles at Cornell University.
• CERN Document Server, a huge, open-access repository of data (articles, theses, ...).
• Atomic Energy Collection at Oregon State University.
• CODATA Committee on Data for Science and Technology.
• Constants, units, ... at NIST (National Institute of Standards).
• Constants of Physics and Mathematics.
• HyperPhysics. An amazing physics database at Georgia State University.
• INSPIRE, High Energy Physics (HEP) information system.
• Karlsruhe Nuclide Chart, maintained by Nucleonica
• Calculator++, a cross-platform (Java) arbitrary-precision calculator.
• Martindale's Geoscience Center..
• Martindale's Physics Center. Amazing.
• Nucleonica an official EU nuclear-science website maintains the famous Karlsruhe Nuclide Chart
• PACS. Physics and Astronomy Classification Scheme (managed by AIP).
• Particle Data Group, an "official" reference organization.
• Physical constants and Astronomical data at University of Wisconsin.
• Physical Reference Data. at NIST (National Institute of Standards).
• SI Units and Prefixes.
• SI Dimensions of Physical Quantities. Over 200 quantities in 22 categories.
• Table of Isotopes at Berkeley.
• UFO sightings.
• Universal Nuclide Chart from Nucleonica (a site maintained by the EU).
• Stan's Library, an online e-Zine edited by Stan Sykora, with a physics section.
• Books lists, Courses, Lecture notes, and similar resources:
• Free online physics books, a list maintained by Stan Sykora.>
• Feynman Lectures on Physics by Richard P.Feynman, R.B.Leighton, and M.Sands, at CalTech.
• Free Online Textbooks, Lecture Notes, Tutorials, and Videos on Mathematics.
  See the Physics section.
• FreeScience directory of free, online physics books.
  Very valuable resource, thought it counts as books also courses and scripta.
• Mathematical Physics, of Alex Stefanov's math books list at the Trillia Group site.
• MIT Open Courses in Nuclear Science and Engineering. Free.
• MIT Open Courses in Physics. Free.
• Online Lectures at Kavli Institute of Theoretical Physics. Great Science available for free.
• Online physics textbooks by Benjamin Crowell. College level. Free.
• Open source Earth Sciences Textbooks at Textbook Revolution.
• Open source Physics Textbooks at Textbook Revolution.
• Physics Books, a list compiled and maintained by Stan Sykora.
• Physics books on eKnigu in PDF and DjVu fomats. Hundreds of items.
• Physics NetBase, a site of CRC Press.
  They give nothing for free but they sure have their physics books and articles well classified.
• Project Gutenberg Astronomy Bookshelf.
• Project Gutenberg Physics Bookshelf.
• Scribd directory of free, online physics books.
• Tech Books for Free Science section.
• Textbooks in Mathematics by Alex Stefanov
  lists many free, online Mathematical Physics and Applied Mathematics books.
• Lists of References:
• Link Directories
• BUBL Link. A collection of physics links, each with a brief description.
• Light Sources, a worldwide directory of accelerator-based sources of EM waves.
• NMR, MRI, NQR and ESR links. Manually managed Magnetic Resonance Directory
• Supernova Pages on the WWW by M. Montes.

Physics HISTORY

• A Brief History of Quantum Mechanics. Appendix to The Strange World of Quantum Mechanics by Dan Styer.
• Biographical memoire of Kenneth T.Bainbridge by Robert V.Pound and Norman F.Ramsey. Mass spectroscopy, Photomultiplier.
• Biographical memoire of R.H.Dicke by W.Happer, P.J.L.Peebles, and D.T.Wilkinson. Quantum theory, Relativity.
• Marconi Society. A great source of information about Guglielmo Marconi.
• Mechanism of the Heavens, a free on-line book by Mary Somerville (1831),
  made available by Malaspina Great Books. 2nd Edition, prepared by Russell McNeil.
• Nuclear Files. Project of the Nuclear Age Peace Foundation. Amazing.
• PV Scientific Instruments. Reproductions of historic instruments.
• Smithsonian Institution. Museums + much more.
• The Hebel-Slichter Effect, a historic and educational essay by Stan Sykora.

PIONEERS of Physics

• MacTutor History of Mathematics archive at St.Andrew's University. Many mathematicians were also Physicists, and vice versa. This is an excellent place to start looking for biographies.

Physics PRIZES

• Nobel Prizes in Physics. See also the complete list.

SOCIAL ASPECTS of Physics

• The Modern Revolution in Physics, an online book by Benjamin Crowell.

EDUCATION and Fun

• A list of free online physics books, courses and theses
• Ad Astra Ltd and Early History of Gravity Engineering, an amusing article by Stan Sykora.
• Consciousness, Physics, and the Holographic Paradigm.
  by A.T.Williams. Unusual, stuffed with links and poetry. Worth pondering.
• Extra-Terrestrial Intelligence. A collection of serious articles.
• Java Applets on Physics. Great, multilingual undergraduate resource from Walter Fendt.
• Java Applets on Astronomy. Great, multilingual undergraduate resource from Walter Fendt.
• Khan Academy, open-source physics videos and lessons. Amazing!. See also.
• List of physics laws, rules and other topics in physics and astronomy, by Eric Max Francis.
• Magnetismus A-Z, amazing and well done hypertext dictionary of magnetics - in German.
• MIT Open Courses in Nuclear Science and Engineering. Free.
• MIT Open Courses in Physics. Free.
• MERLOT. An amazing educational resource.
• Online Lectures at Kavli Institute of Theoretical Physics. Great Science available for free.
• Physics lectures by Fritz Bosch. A few are in English, most in German.
• Servizio dispense presso Dipartimento di Fisica, Uni Roma1. Italiano.
• Superconductors information for Beginners. An excellent web site.
• TeachSpin. Small instruments for teaching Science (mostly physics).
• TelAtomic. Small instruments for teaching Science (mostly physics).
• Textbooks in Mathematics by Alex Stefanov
  lists many free, online Mathematical Physics and Applied Mathematics books.
• The Gibbs Paradox, an interesting 1996 article by E.T.Jaynes.
• The Hebel-Slichter Effect, an educational article by Stan Sykora.
• The Science of Spectroscopy for the advanced.
• Thermal Physics course by Michael Gershenson (Rutgers Uni).
• Thermodynamics, lecture notes by Zoltan S.Spakovszky (MIT). Exhaustive and excellent.
• Thermodynamics & Statistical Mechanics, lecture notes by Richard Fitzpatrick (Uni Texas at Austin). Very extensive, HTML only.
• Upscale by David M. Harrison (Uni Toronto).
  Undergraduate Physics Students' Computing and Learning Environment.
• Video Lectures on The Best Physics Videos.
• Fun:
• APS Outreach program.
• Best Physics Videos, a really huge collection.
• Eye tricks. Most amusing.
• Flash animations for physics by David M. Harrison. Formidable.
• Geek stuff shop. See air-zooka, romp pendulum, etc...
• Phun Physics from the University of Virginia.
• Physlink Science e-Store. Science gadgets for kids. Great.
• Physicists jokes at WorkJoke.
• Planetary puzzles and crosswords collected by Calvin J.Hamilton.
• Science poetry & fun corner in Stan's and Lucia's Log Cabin.
• Science poetry inspired by Astronomy by Stuart Atkinson.
• The Living Moon, by Pegasus Research Consortium.
• The Ultimate Guide to Optical Illusions. Nice.

INFO ... Articles, Papers, Personal websites, ...

• Common Data Format (CMD) - a Physics XML supported by NASA.
• Eric Weisstein's physics pages at Mathematica. Excellent.
• Integrity Research Institute. Many out-of-the-chorus articles.
  Zero-point energy, space-worthy propulsion, etc.
• Philosophy of Science Archives at University of Pittsburg.
  Lots of free articles; many about interpretation of quantum physics (over 500 items).
• Solar constant. A brief review by Claus Frölich with 9 references.
• The Official String Theory Web Site.
• Unusual Research home page. Links to out-of-the-chorus articles.
• Personal websites of physicists.
  Note: any comments of mine are purely subjective and possibly whimsical.
• John Baez. A great website of a mathematical physicist.
• Dan Styer (Oberlin, Ohio). Quantum physics.
• Albert Tarantola. Lots of articles. Good stuff.
• Articles and other free online texts:
• Articles by Albert Tarantola:
     Popper, Bayes and the Inverse Problem,
     Probabilistic Approach to Inverse Problems (with Klaus Mosegaard)
     Mathematical Basis for Physical Inference (with Klaus Mosegaard)
     Monte Carlo Sampling of Solutions to Inverse Problems (with Klaus Mosegaard)
     Inverse Problems = Quest for Information (with Bernard Valette)
     Generalized Nonlinear Inverse Problems Solved using the Least Squares Criterion (with B.Valette)
     Three-Dimensional Inversion Without Blocks (with Alexandre Nercessian)
     Theoretical Background for the Inversion of Seismic Waveforms
     Nonlinear Inversion of Seismic Waveforms (with Marwan Charara and Christophe Barnes)
     Noninformative Probability Density for the Elastic Tensor
     The Mathematics of Continuity
     A Maxwellian Theory of Gravitation
  and more ...
• Generating Ontology: From Quantum Mechanics to Quantum Field Theory by Edward MacKinnon.
• Is every finite-dimensional Hilbert space a spin-space ?, an article by Stan Sykora.
• Notes by Peter Diehr:
     Notes on Analytical Mechanics, 57 pages
     Notes on Rigid Body Dynamics in SO(3)
• Symmetries and Reflections, an essay by E.P.Wigner.
• Why are there 63360 inches per mile?, John Baez.
• How Many Fundamental Constants Are There?, by John Baez.

Astronomy

• Abrams Planetarium at Michigan State University. They have a nice skywatcher's pages.
• Anglo-Australian Observatory at Epping, NSW (Australia).
• Astronomical Observatory of Bologna.
• Astronomy Thesaurus by the Shobbrooks.
• Astrophysics & Cosmology at Particle Data Group.
• ESA. European Space Agency.
• ESO. European Southern Observatory.
• Hubble heritage project. Don't miss the image gallery page.
• Hubble telescope site.
• Isaac Newton Group of Telescopes (ING) at La Palma (Spain).
• Joint Astronomy Center in Hawai (run by STFC).
• Jodrell Bank Centre for Astrophysics at Uni Manchester, (UK).
• La Silla Paranal Observatory in Chile (run by ESO).
• MERLIN / VLBI the Multi-Element Radio Linked Interferometer Network National Facility, (UK).
• NASA. National Space Agency.
• NASA Image Galleries.
• NRAO National Radio Astronomy Laboratory.
• Rice University Space & Physics.
• SOHO images of the Sun. Near real time and historic.
• Solar eclipse video at the Pakistani Khwarzimic Society web site.
• Sky almanac for skygazers at Star Date magazine (Texas).
• Supernova Pages on the WWW by M.Montes. Amazing collection of links.
• Spitzer Space Telescope's CalTech site.
• The Worlds of David Darling. Astronomy, Space, Alternative energy, Sustainable living.
• Views of the Solar System collected by Calvin J.Hamilton.
• WorldWide Telescope, a nice initiative by Microsoft Research.
• Star catalogues and maps:
• Project Rho starmaps. Intriguing.

Space exploration

• ASI, Agenzia Spaziale Italiana.
• ESA. European Space Agency.
• Extrasolar Planets Encyclopaedia mainained by Jean Schneider. Excellent.
• JPL. Jet Propulsion Laboratory.
• JPL Near-Earth Objects Program.
• JPL near collision simulation.
• JPL Photojournal. Planets etc.
• NASA/Image Galleries.
• NASA/JPL. Jet Propulsion Laboratory.
• NASA/JSC. Johnson Space Center.
• NASA/KSC. Kennedy Space Center.
• NASA/MSFC. Marshall Space Center.
• NASA/JPL. Space events calendar.
• NASA/Spacelink.
• NASA Planetary home page.
• Rice University Space & Physics.
• Science poetry inspired by Space exploration by Stuart Atkinson.
• Space.com at Imaginova Corp.
• SpaceShip One. First successful private spaceship.
• Virgin Galactic. First private space-travel Company.
• Watch on NASA. Not NASA - they just keep an eye on them!
• Extra-Terrestrial Life and/or Intelligence
• SETI. Search for Extra-Terrestrial Intelligence.
• SETI at home and on your PC! Software download!
• Invitation to ETI. Exciting.
• Extra-Terrestrial Intelligence. A collection of serious articles.

Spectroscopy

• Fellgett's advantage on Wikipedia.
• Fourier transform infrared spectroscopy on Wikipedia.
• The Advantages of FT-IR Spectroscopy, a brief article by Frank Antolasic.

Alternative Physics: history will show whether they are Nobel-prize worth or jusst cranks

• American Antigravity, a non-profit organization with a dream.
• Alternative Physics website of Bernard Burchell.
• Cliff Pickover's website (mathematician and speculative physicist).
• Crypts of Physics by Hans van Leunen. This is his home page,
  where he wraps-up his (heavily promoted) Hilbert Book Model.
• Faster-than-light article on Wikipedia.
• FQXi, a speculative Physics forum on Foundational Questions Institute.
• Non-standard cosmologies on Wikipedia.
• Tired light theories on Wikipedia.
• Superluminal motion on Wikipedia.
• The Faraday group promotes deterministic quantum mechanics.

SOFTWARE

• Free, online:
• Calc98, pretty good and free multi-mode calculator.
  There is also a reduced-functionality online version (jCalc).
• C++ QED project on sourceforge.
• Digital Dutch web converter for basic physical quantities by J.D.Stegeman. Simple and elegant.
• Digital Dutch 1976 standard atmospherecalculator by J.D.Stegeman.
• Free, opensource and low-cost:
• Free Online Textbooks, Lecture Notes, Tutorials, and Videos on Mathematics.
  See the Software section.
• Graph paper to print. Various formats.
• MathStudio a great low-cost graphing and symbolic math app for mobiles and Windows.
  Goes also under the name SpaceTime.
• MegaConverter of measurement units.
• Octave, a free Matlab-compatible (almost) package and public project. Excellent.
• SCILAB, a free and good competitor of MATLAB.
• Steam tables online calculators.
• Commercial software:
• Comsol Multiphysics simulation environment. Rather good, but expensive.
• MAGMA home. Magma is a major computational algebra system. Expensive.
• MapleSim at MapleSoft. Multi-domain modeling and simulation. Expensive.
• Matlab home. We all use it at least sometimes, of course. Expensive.

COMPANIES

Separate page: Magnetic Resonance Companies, Magnets and Magnetics

• Cenco Physics. An educational and home-science instrumentation supermarket.
• MapleSoft, home of MapleSim and Maple.
• MathSoft. Home of Matlab.
• Ocean Optics. Affordable VISIBLE, UV and IR spectrometers and optics.
  USB instruments, spectrometers for education, etc.
• Physlink Science e-Store. Science gadgets for kids. Great.
• PV Scientific Instruments. Reproductions of historic instruments.
• qutools. Quantum photonics devices. Quantum entanglement demonstrator!
• TeachSpin. Small instruments for teaching Science.
• TelAtomic. Small instruments for teaching Science.

SANDBOX for items yet to be sorted

• Article: neutrinos, matter and antimatter.
• Paper: antenna near-field.
• Article: IBM logo made from atoms.
• Video: IBM logo made from atoms.
• Paper: fundamental constants in high gravity.
• Augros presentation: A 'Bigger' Physics.
• Article: on Engineering Inspiration (Materials etc ?).
• Article: on Science 4 All, on colors.
• List of papers by Hanggi on relativistic Brownian motion and thermodynamics.
• Maxwell equations.
• Space Frontier Foundation.
• Book to be: by Hans de Vries, on relativistic QFT.
• Presentation by Morganti: On active galactic nuclei.
• Book: Coherence. Free, online PDF. Very good.
• Google books: The Historical Development of Quantum Theory.
• Home page of Stefano Liberati.
• Article: Scientific method: Defend the integrity of physics.
• Article: Quantum effects get a weirdness scale.
• Hans de Vries on Fine Structure Constant.
• Article: on equivalence principle.
• Article: on invisibility.
• Shuttle factor.
• Article: Nonlocal correlations between the Canary Islands.
• Article on SETI: Looking For Deliberate Radio Signals From KIC 8462852.
• Spectral Calculator. Very good.
• Japanese spectroscopy database.
• Wikipedia: list of effects.