- A Crash Course in the Mathematics of Infinite Sets - A introductory guide for philosophers by Peter Suber, explaining the use of infinitary set theory.
- A New System of Axioms Instead of ZF - The page claims that "the axioms shown below have the contents that should overturn the set theory of today".
- Axiom of Choice and Continuum Hypothesis - Part of the Frequently Asked Questions in Mathematics.
- Bounded Set Theory - A weak version of ordinary set theory using bounded quantification. Papers and software.
- Cantor's Theorem - Article in the Platonic Realms, describing Cantor's diagonal argument that proved that infinity comes in many different 'sizes'.
- 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.
- Equivalence Relation - Encyclopedia entry on equivalence relations and their role in set theory.
- Extending Set Theory - Extends the language of set theory through restricted self-reference and through certain large cardinals. Also discusses higher order set theory and axiomatization through reflection principles.
- Infinite Ink: The Continuum Hypothesis, by Nancy McGough - History, mathematics, metamathematics, and philosophy of Cantor's Continuum Hypothesis
- Metamath Proof Explorer - Over 3000 complete formal proofs deriving numbers and beyond from Zermelo-Fraenkel set theory axioms.
- 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.
- Operational Set Theory - Description, errata and reviews of a book by Luis E. Sanchis.
- Programming with Sets - Using set-theoretic primitives as a conceptual tool in programming, includes discussion of SETL and MIRANDA languages.
- Set Theoretic Analysis. - On a part of math where Set Theory, Topology and Analysis meet. Has surveys, preprints, conference announcements, book reviews and problems.
- Set Theorists - A list of email addresses and affiliations.
- Set Theory - Directory of set theorists, maintained by Jean A. Larson.
- Set Theory - Survey from the Stanford Encyclopedia of Philosophy by Thomas Jech.
- Set Theory - From Dave Rusin's "Known Math" collection.
- Set Theory for the Working Mathematician - Krzysztof Ciesielski, CUP (1997). Contents and preface.
- Set Theory Page - Collection of links related to set theory.
- Sets and Their Sizes - An alternative to Cantor's theory of cardinality. Dissertation by Fred M. Katz.
- Shelah's Archive - Listing of all articles by Saharon Shelah, and links to many of them.
- The Axiom of Choice - This page gives a brief explanation of the Axiom of Choice and links to other related websites.
- The Beginnings of Set Theory - MacTutor History of Mathematics topic.
- The Future of Set Theory by S. Shelah - The text of a talk given around the millennium.
- The Mathematics of Set Theory - Detailed description of parts of introductory set theory.