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

For a more generic Directory, see the Stan's links to Science Institutions.

• International:
• International Mathematical Union ().
• International Mathematical Sciences Institutes list maintained by Fields Institute.
• ISI, the International Statistical Institute.
• Math-Net, an International Information and Communication System of the IMU.
• MSC 2010, the home site of the Mathematics Subject Classification.
• W3C MathML. Home of the Math Markup Language.
• Europe:
• Abel Prize web site.
• Center for Innovation in Mathematics Teaching (CIMT) at Uni Plymouth, UK.
• Center for the Popularization of Mathematics (CPM) at Uni Wales, Bangor, UK. Great!
• Czech Mathematical Society. Czechs, click here.
• European Mathematical Information Service (EMIS).
• European Mathematical Society (EMS). New website!
• Institute of Mathematics of the Czech Academy of Science in Prague.
• Isaac Newton Institute for Mathematical Sciences in Cambridge, UK.
• London Mathematical Society (LMS).
• USA:
• American Mathematical Society (AMS). Entry door to the expensive MathSciNet.
• Center for Mathematics and Science Education (CMSE) at North Carolina University.
• Clay Mathematics Institute in Massachussets. Supports mathematics and awards prizes.
• MAA, the Mathematical Association of America.
• MSRI, Mathematical Sciences Research Institute at University of Berkeley (California) and supported by NSF.
• Netlib Repository of mathematical software, papers, and databases.
  There is also a netlib mirror at Sandia National Labs.
• NIST's Math pages. Excellent.
• NSF Mathematical Sciences Institutes, a list and an access portal to all 7+ of them.
• Elsewhere:
• Bhaskaracharya Institute of Mathematics in Pune, India.
• Fields Institute in Toronto, Ontario, Canada.
• Australian Mathematical Sciences Council (AMSC), Australia.
• Australian Mathematical Society (AustMS), Australia.
• Institute for Mathematical Sciences (IMS), Singapore.
• National Committee for the Mathematical Sciences (NCMS)
  of the Australian Academy of Sciences.
• Statistical Society of Australia (SSA), Australia.
• WuHan Institute of Physics and Mathematics of the Chinese Academy of Scieces.
  english version.

JOURNALS, e-Zines, Forums, Libraries and Blogs

• AMS Journals.
• Biometrica. Despite the name, this Journal covers most of applied statistics.
• Czech Digital Mathematics Library offers open access to Czechoslovak Mathematical Journal, Applications of Mathematics, Archivum Mathematicum, Commentationes Mathematicae Universitatis Carolinae, and the Bolzano Collection.
• Math journals. A list maintained by AMS n(with links).
• MathDL, the MAA Digital Library.
• Open Access Mathematics Journals. Last count: 150.
• Plus Magazine ... living mathematics. A popularization initiative.
• Scientific Computing.
• e-Zines and Forums
• Convergence, where mathematics, history and teaching interact. An MAA magazine.
• Math Forum, dedicated to math teaching. Drexel University, Philadelphia.
• Math Forum library, a nice online resource.
• Mathematics at About.com.
• Plus. A nice math e-zine.
• Topology Atlas, a publisher of information related to topology.
• Blogs and personal forums:
• Abstract and Linear Algebra Forum of Edwin Connell.
• Deb Russell's blog on About. Strong in teaching and social aspects.
• Gyre&Gimble, observations on math, language and other things by Charles Wells.
• Un blog di matematica di Maurizio Codogno (in italiano).
• Jiri Lebl's blog on Wordpess.
• Mathematics Journals blog of John Ewing. Great reflections about scientific publishing.

ENCYCLOPEDIAs, Dictionaries and Wikis

• Online Encyclopedia of Mathematics by Eric Weisstein.
  See also the Mathworld site.
• Math Dictionary at Future School. Basic level.
• Mathwords. A simple illustrated Math dictionary. Basic level educational; well done.
• Wikis:
• Mathematics on Wikipedia.
• Mathematics on Wiki Slice. Very informative.
• Mathematical Software review on Wiki Slice. Very informative.
• Mathematics Subject Classification Wiki. NEW: MSC 2010.

DATABASES, Directories and Reference lists

• ACM Digital Library Portal.
• Constants of Mathematics and Physics.
• Czech Digital Mathematics Library offers open access to the metadata and fulltext of mathematical journals, proceedings and books published throughout history in the Czech lands. Excellent!
• DADS. Dictionary of Algorithms and Data Structures at NIST.
• Handbook of Mathematical Functions by M.Abramowitz, A.Stegun, Editors.
• Math at arXive, math articles at arXive. Huge and free. See also Front for arXive.
• Mathematics Articles on Wikipedia, an extensive index.
• Mathematics Subject Classification, MSC (from AMS).
• National Curve Bank at California State University,
  managed by Shirley Gray, Stewart Venit, and Russ Abbott. There is much more than just famous curves. Amazing.
• Sloane's database of integer sequences. 127289 entries !!!
• Statistics articles repository at arXive. Free.
• Wolfram MathWorld constants on the Eric Weissstein's site.
• Link Directories:
• BUBL Link. An amazing collection of math links, each with a brief description.
• Infinite Exponentials and Tetration. Collection of links.
• Math and Reading Help for Kids, a nice directory of math-education articles, games, etc.
• Math Forum library, a nice online resource (links).
• Math Help for all Grades, a nice directory of math-education articles.
• Math Journals. A list of Journals maintained by AMS n(with links).
• Math-Net Links to the mathematical world.
• Number Theory Web. Vancouver, Rome, Cmbridge, Tokyo.
• Platonic Solids links collected by Dan Radin.
• Webring of Mathematics.
• Books lists and similar resources:
• Alex Stefanov's list, modified and updated at the Trillia Group site. original version is still accessible at 100MB.
• AMS Books Online. Many are free or at least there are freely dowloadable Chapters.
• Cornell University Library Historical Math Monographs. Open-access resource. Excellent.
• EMS Publishing House.
• Free Online Books on Mathematics.
• Free Online Textbooks, Lecture Notes, Tutorials, and Videos on Mathematics.
  Great and serious.
• FreeScience directory of free, online mathematics books.
  Very valuable resource, thought it counts as books also courses and scripta.
• Math Forum library, a nice online resource (links).
• Math at the MIT Open CourseWare initiative. Free courses and books.
• Mathematics Books, a list compiled and maintained by Stan Sykora.
• Mathematics books on eKnigu in PDF and DjVu fomats. Hundreds of items.
• MSRI books on the Mathematical Sciences Research Institute site.
  These are thematic collections of articles available both online and in print.
• Online Mathematics Books. List of free Math books on the web edited by Stan Sykora.
• Online Mathematics Textbooks, links to 65 on-line math texts collected by George Cain.
• Open source Mathematics Textbooks at Textbook Revolution.
• Online math books by R.B.Ash (Uni Illinois). Seven free www books and Courses.
• Textbooks in Mathematics, collected by Alex Stefanov.
  A list of links to free, online math textbooks.
• Reference lists:
• Numbers, constants and computation by X.Gourdon and P.Sebah. 223 references. Nice.
• Papers by James Milne. Elliptic curves, groups,fields, cohomology, ...
• Papers by C.Pomerance. Number theory, prime numbers. 135 entries.

PRIZES and Pioneers

• Fields Medal, considered the highest award in Mathematics.
• IMU Medals. Prizes awarded by the International Mathematical Union.
• Pioneers:

HISTORY

• Cornell University Library Historical Math Monographs. Open-access resource. Excellent.
• Earliest Known Uses of Some of the Words of Mathematics,
  a project managed by Jeff Miller. Amazing.
• Earliest Uses of Symbols of Operation, a project managed by Jeff Miller. Amazing.
• History of Mathematics by David E. Joyce.
• Home site of K.Podnieks. Very good.
• Images of Mathematicians on Postage Stamps, collected by Jeff Miller.
• Portrait Gallery of Mathematicians at MAA.
• St.Andrew's University archives. Excellent.

SOCIAL aspects

• Convergence, where mathematics, history and teaching interact. An MAA magazine.
• Deb Russell's blog on About.com. Strong on math teaching.
• Math + Religion = Trouble by Ron Csillag.
• What does "DOING MATH" mean? by Keith Devlin.

EDUCATION and Fun

• A list of free online mathematics books, courses and theses
• Abstract Math website, managed by Charles Wells. Excellent.
• Ad Astra Ltd and Early History of Gravity Engineering by S.Sykora
  is an amusing example of applied variational calculus.
• AP Statistics Review App for iPod/iPhone.
• Art of Problem Solving for students and their parents and teachers.
• Center for the Popularization of Mathematics (CPM) at Uni Wales, Bangor, UK.
  Great, especially on knots and sculpture.
• Complex Analysis Project for undergraduates by John H.Mathews. See the modules.
• Encyclopedia of Mathematics by E.Weisstein.
• Geometry in Action on the site of David Eppstein. Amazing and useful.
• Home site of Erich Friedman. Amazing excellent educational site.
• Home site of David E. Joyce.
• Khan Academy, open-source Math and Science videos and lessons. Amazing!. See also.
• Learn Math Online, a very nice and free resource for math teachers and students
  from kindergarten to high school.
• Math Forum library, a nice online resource (links).
• Math at the MIT Open CourseWare initiative. Free courses and books.
• Math Help for all Grades, a nice directory of math-education articles.
• Math Online, a nice Gallery of college-level applets, puzzles, ... at Uni Wien, Austria.
  Also im Deutch (the German version is much more complete).
• Math Planet, nice lectures and free short videos for kids.
• Math Playground, lots of stuff for kids aged 5-14.
• Mathematical Means and Averages: Basic Properties, a primer by Stan Sykora.
• MathCS, resources for anyone interested in Mathematics, Statistics, Java Programming, or Robotics.
• Mathematics Articles on Wikipedia, an extensive index.
• MIT Open Courses in Mathematics. Free.
• National Curve Bank managed by S.Gray, S.Venit, and R.Abbott at California State University,
  There is much more than just famous curves. Amazing.
• Numerical Analysis Project for undergraduates by John H.Mathews. See the modules.
• Numericana of G.P.Michon. An excellent educational site.
• Polygons and Polyhedra of Bob Alanson. Nice educational site.
• Precalculus Review App for iPod/iPhone.
• Taylor Traitor Functions an article on the dangers of Taylor expansions.
• Vasar Stats, a nice resource on statistics.
• Virtual Math Museum maintained by R.Palais. Amazing.
• Wikipedia entry on Mathematics.
• Fun:
• A simple solution to the Monty Hall problem by Jeffrey S.Rosenthal.
• Amusements in Mathematics, a shareware e-book by Henry E.Dudeney.
• Ananthapuri Mathematics jokes.
• Astounding Math Stories by Charles Wells.
• Books by Ian Stewart:
  - Game, Set and Math: Enigmas and Conundrums
  - Why Beauty Is Truth: A History of Symmetry
  - How to Cut a Cake: And Other Mathematical Conundrums
  - Math Hysteria: Fun and Games with Mathematics
  - The Science of Discworld, I
  - The Science of Discworld II: The Globe,
  - The Science of Discworld III: Darwin's Watch
  - Another Fine Math You've Got Me Into ...
  - Nature's Numbers: The Unreal Reality Of Mathematics
  - Does God Play Dice? The New Mathematics of Chaos
  - From here to Infinity
  - Letters to a Young Mathematician (Art of Mentoring)
• FunFacts at Harvey Mudd College. Excellent!
• Inverse Graphing Calculator on the nice edu site of Sam Alexander.
• Math humor at Uni Utah.
• Math puzzles made or collected by David E. Joyce:
  Dave's Square Dissection puzzles,
  Dudeney's Catching the Mice puzzle,
  Shasha's Surprizing Strings puzzle,
  Hickerson's Prime Maze puzzle.
• Mathematical Art at the Virtual Math Museum. Amazing.
• Mathematics and Sex; a book by Clio Cresswell.
• Platonic Solids site of Dan Radin. Great.
• Recreational Math, collected and created by David Eppstein.
• Some Math Quotes collected by S.Bilaniuk.
• Sheppard software. They make learning fun. Online games!
• The Geometry Junkyard, collected by David Eppstein.
• XKCD comics.
• Famous and/or Unsolved math Problems
• Mathematical Problems by David Hilbert, the famous Lecture delivered before the International Congress of Mathematicians at Paris in 1900, edited for the web by David E. Joyce.
• Unsolved problems at MathWorld.

INFORMATION Sources, Libraries, Articles, ...

• Arithmetic Duality Theorems by James S.Milne. Available also in printed form.
• Cornell University Library Historical Math Monographs. Open-access resource. Excellent.
• Essential Mathematica for Students of Science. A Tutorial Approach to Mastery of Mathematica by James J.Kelly.
• Geometry, Surfaces, Curves, Polyhedra at the site of Paul Bourke. Amazing.
• Handbook of Mathematical Functions by Abramowitz M., Stegun A., Editors.
• Home site of Sam Alexander is a mix of fun and education.
• Home site of John Baez.
• Home site of Ioannis Galidakis.
• Home site of Jim Hefferon at Saint Michaels' College. Very useful.
• Home site of David Joyce.
• Home site of Jiri Lebl.
• Home site of late J.F.MacDonnell with its nice treatement of the hyperpower function.
• Home site of J.Peter May. A great source on topology.
• Home site of James Milne (Ann Arbor, New Zealand). Elliptic curves, groups,fields, cohomology, ...
• Home site of Hans D.Mittelmann. A treasure trove on numerical math and optimization methods.
• IEEE 754. Floating point format.
• Infinite Ink. The continuum hypotheses.
• Interactive Mathematics. Math pages at Ngee Ann Polytechnic in Singapore.
• Math at arXive, math articles at arXive. Huge and Free. See also Front for arXive.
• Math Topics.
• Mathematical Illustrations by Bill Casselman. Very good.
• Mathematical Constants by Steven Finch, plus a lot more. Many PDF's. Excellent.
• Mathematics Genealogy Project at North Dakota State University.
• Numbers, constants and computation by X.Gourdon and P.Sebah. Nice.
• Numericana of G.P.Michon. A rich source of information from magnificient to mundane.
• On-Line Encyclopedia of Integer Sequences by N.J.A.Sloane et al. 127289 entries !!!
• Online mathematics books. List of free Math books on the web.
• RGMIA, Research Group in Mathematical Inequalities at Victoria University.
• Wolfram MathWorld. The web's most extensive mathematics resource, at Wolfram Research.
• Libraries:
• Stan's Library section on mathematics.
• Reprints in Theory and Applications of Categories. 18 free articles and books.
• Virtual Math Library. Very useful!
• Some interesting articles:
• Approximations of Ellipse Perimeters. A Review with further references and links.
• 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)
  = Generalized Nonlinear Inverse Problems Solved using the Least Squares Criterion (with B.Valette)
  = Three-Dimensional Inversion Without Blocks (with Alexandre Nercessian)
  = Noninformative Probability Density for the Elastic Tensor
  and more ...
• Binary Iterated Powers. Novel concept.
• Comparison of computer algebra systems, an useful article on Wiki Slice. Lots of up-to-date links.
• Mathematics Articles on Wikipedia, an extensive index.
• MSRI books on the Mathematical Sciences Research Institute site.
  These are thematic collections of articles available both online and in print.
• Numerical methods for the inversion of the Laplace transform,
  a very nice page maintained by Peter Valkó.
• Surface Integrals over n-Dimensional Spheres.
• Volume Integrals over n-Dimensional Ellipsoids.

SPECIAL Topics

• Wavelets:
• Wavelets - all there is to know about them. Do not miss this resource!
• Wavelets, a 50-page paper (almost a book) by Ronald DeVore and Bradley Lucier.

SOFTWARE

• Free, open source and low-cost:
• Computing and a lot of other stuff by G.Urroz.
• Free Online Textbooks, Lecture Notes, Tutorials, and Videos on Mathematics.
  See the Software section.
• Mathematical Software review on Wiki Slice. Very informative.
• MathPlayer. Plugin for Internet Explorer to read MathML. Free.
• Netlib Repository of mathematical software, papers, and databases.
  There is also a netlib mirror at Sandia National Labs.
• NTL: A Library for doing Number Theory by Victor Shoup.
• PARI/GP algebraic computing system (particularly number theory).
  See also a PARI/GP tutorial by Robert B. Ash.
• R Project; free environment for statistical computing. Unix, Windows, MacOS.
• S-Plus from Insightful (expensive).
• SAGE, a free mathematics software system licensed under the GPL. Uses Python.
• SCILAB, a free and good competitor of MATLAB.
• StatLib. Data, Software and News from the Statistics Community.
• Vasar Stats: Excellent website for statistical computation (by R.Lowry).
• Commercial software:
• Mathematica home (Wolfram Research). An expensive symbolic-math jewel - plus a great, free math database.
• MAGMA home. A major computational algebra system. Expensiv
• Maple home. Another major software packege to do Math. Expensive.
• MathType home. Professional version of Microsoft's Equation Editor.
• Matlab home (MathSoft). We all use it at least sometimes, of course. Expensive.

COMPANIES

• Design Science. Home of MathType, MathFlow and MathPlayer.
• MapleSoft, home of Maple and MapleSim.
• MathSoft. Home of Matlab.
• Wolfram Research. Home of Mathematica. The Company created by Stephen Wolfram.

EVENTS: Conferences, Meetings, ...

• ICM. Next International Congress of Mathematicians.
• Fields Institute calendar of events.
• Isaac Newton Institute for Mathematical Sciences workshops and events list.
• NSF Mathematical Sciences Institutes' list of upcoming events.
• Future events in chronological order:
• Past events in reverse chronological order:
• 5-th European Congress of Mathematics
  was held July 14-18, 2008, in Amsterdam, Netherlands.
• SAC 2008, the 23th Annual ACM Symposium on Applied Computing,
  was held March 16-20, 2008, in Fortaleza, Brazil.
• SAC 2009, the 24th Annual ACM Symposium on Applied Computing,
  will be held March 8-12, 2008, in Honolulu, Hawaii, USA.