Infinite Ink: The Continuum Hypothesis, by Nancy McGough  
   History, mathematics, metamathematics, and philosophy of Cantor's Continuum Hypothesis
   http://www.ii.com/math/ch/

The Axiom of Choice  
   This page gives a brief explanation of the Axiom of Choice and links to other related websites.
   http://math.vanderbilt.edu/~schectex/ccc/choice.html

Set Theory Page  
   Collection of links related to set theory.
   http://www.cis.syr.edu/~sanchis/setory.html

The Beginnings of Set Theory  
   MacTutor History of Mathematics topic.
   http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/Beginnings_of_set_theory.html

A Crash Course in the Mathematics of Infinite Sets  
   A introductory guide for philosophers by Peter Suber, explaining the use of infinitary set theory.
   http://www.earlham.edu/~peters/writing/infapp.htm

Set Theory People  
   Directory of set theorists.
   http://cid.unomaha.edu/~aroslano/people.html

New Foundations  
   Set theory introduced by W. V. O. Quine in 1937. This is a refinement of Russell's theory of types based on the observation that the types in Russell's theory look the same, as far as one can apparently prove.
   http://math.boisestate.edu/~holmes/holmes/nf.html

Bounded Set Theory  
   A weak version of ordinary set theory using bounded quantification. Papers and software.
   http://www.botik.ru/~logic/bst/bst.html

Issues in Commonsense Set Theory  
   Paper by Müjdat Pakkan and Varol Akman
   http://www.cs.bilkent.edu.tr/~akman/jour-papers/air/air.html

Programming with Sets  
   Using set-theoretic primitives as a conceptual tool in programming, includes discussion of SETL and MIRANDA languages.
   http://www.CS.NMSU.Edu/~complog/sets/

Set Theoretic Analysis.  
   On a part of math where Set Theory, Topology and Analysis meet. Has surveys, preprints, conference announcements, book reviews and problems.
   http://www.math.wvu.edu/~kcies/STA/STA.html

Set Theorists  
   A list of email addresses and affiliations.
   http://www.cs.elte.hu/~kope/setad

Set Theory for the Working Mathematician  
   Krzysztof Ciesielski, CUP (1997). Contents and preface.
   http://www.math.wvu.edu/~kcies/STbook.html

Operational Set Theory  
   Description, errata and reviews of a book by Luis E. Sanchis.
   http://www.cis.syr.edu/~sanchis/operational.html

Cantor's Theorem  
   Article in the Platonic Realms, describing Cantor's diagonal argument that proved that infinity comes in many different 'sizes'.
   http://www.mathacademy.com/pr/prime/articles/cantor_theorem/

The Mathematics of Set Theory  
   Detailed description of parts of introductory set theory.
   http://www.jboden.demon.co.uk/

Set Theory  
   Survey from the Stanford Encyclopedia of Philosophy by Thomas Jech.
   http://plato.stanford.edu/entries/set-theory/

Metamath Proof Explorer  
   Over 3000 complete formal proofs deriving numbers and beyond from Zermelo-Fraenkel set theory axioms.
   http://metamath.org

Axiom of Choice and Continuum Hypothesis  
   Part of the Frequently Asked Questions in Mathematics.
   http://db.uwaterloo.ca/~alopez-o/math-faq/mathtext/node34.html

The Future of Set Theory by S. Shelah  
   The text of a talk given around the millennium.
   http://front.math.ucdavis.edu/math.LO/0211397

Shelah's Archive  
   Listing of all articles by Saharon Shelah, and links to many of them.
   http://shelah.logic.at/

Consequences of the Axiom of Choice Project  
   Project to keep the book (also named in the title), describing forms related to the Axiom of Choice and their implications, updated.
   http://www.math.purdue.edu/~jer/cgi-bin/conseq.html

Equivalence Relation  
   Encyclopedia entry on equivalence relations and their role in set theory.
   http://www.iscid.org/encyclopedia/Equivalence_Relation

Cantor's Donut Paradox  
   Reassessing Uncountability and the Continuum Hypothesis with Reference to a Novel Geometrical Analogue of the Aleph Series.
   http://www.cantorsdonutparadox.co.uk/