Peter Smith’s Logic Matters blog. Logic, philosophy of maths, music, and other enthusiasms. Latest posts: "Frege on "if"" on 14 January; "Scott Aaronson on P ?= NP" on 06 January; "Tom Leinster's Basic Category Theory" on 02 January.
Categories. Links to online resources at an introductory/intermediate level, including lecture notes and freely available books. Also a link to my evolving Gentle Introduction to categories, and to a reading list aimed at philosophers.
The Teach Yourself Logic Study Guide is an annotated reading list for students who want/need to teach themselves more logic than is nowadays provided in many university courses. There are also supplements and Book Notes on various general mathematical logic texts and other books.
Web pages to support An Introduction to Gödel’s Theorems (CUP 2007/2013). Additional materials include exercises, lecture notes ‘Gödel Without (Too Many) Tears’ for philosophers, and two very short courses for mathematicians.
Web pages to support An Introduction to Formal Logic (CUP, 2003; latest corrected reprint 2016). Links to answers to exercises. But also various additional materials, overheads for lectures, worksheets, unpublished chapters.
Notes and Papers. This page links to various notes, handouts, draft papers, book reviews and so on from the last few years, of rather varying levels of sophistication and difficulty (but all should be accessible to those who already know a bit of logic).
Logical snippets, and other advice for students. More logic help and advice in the form of short contributions first posted on math.stackexchange in answer to students’ (mostly elementary) questions. Plus some advice on writing/publishing papers. And some more advice on reading.
The LaTeX for Logicians pages, which give a brief guide to resources of interest to logicians, philosophers and others using LaTeX to produce papers or presentations, teaching materials, theses or books, and perhaps wanting to include logical matter such as natural deduction proofs.