Online resources: * [The Catsters channel][1] * [MATH198 course notes][2] - examples in Haskell * [Rydehard, Burstall: Computional Category Theory][3] - examples in ML (free reprint of a book) * [MAGIC course][4] * [Barr, Wells: Category theory for computing science][5] (TAC TR22 is a free reprint of the book) * [Jaap van Oosten: basic category theory][6] * [Tom Leinster][7] * [Eugenia Cheng][8] * [Steve Awodey][9] - very similar to the book mentioned by Quadrescence * [Daniele Turi][10] * [Thomas Streicher][11] * [Abstract and concrete categories: the joy of cats][12] - might be considered too verbose, but it's full of examples; slightly newer (?) version as [TAC TR17][18] * [Spivak: Category Theory for Scientists][19] - free textbook of a 2013 MIT OpenCourseWare; an updated (and non-free) version was published by MIT Press in 2014. Books (not free): * Benjamin Pierce: Basic category theory for computer scientists, MIT Press 1991; a slight expansion/update of the earlier (and free) [CMU-CS-88-203 report][20] * MacLane - solid mathematical foundations, but hardly any references to computing * [Martin Brandenburg][21] - Einführung in die Kategorientheorie (in german) Category theory in Haskell: * [Wikibooks introductory text][13] * [sigfpe's blog][14] has a lot of category theory articles - (di)natural transformations, monads, Yoneda lemma... * [Comonad.Reader][15] * [The Monad.Reader][16] - check "Calculating monads with category theory" [Another list][17] [1]:http://www.youtube.com/user/TheCatsters [2]:http://haskell.org/haskellwiki/User:Michiexile/MATH198 [3]:http://www.cs.man.ac.uk/~david/categories/book/ [4]:http://www.cs.manchester.ac.uk/~hsimmons/MAGIC-CATS/magic-cats.html [5]:http://www.tac.mta.ca/tac/reprints/articles/22/tr22.pdf [6]:http://www.itu.dk/~birkedal/teaching/category-theory-Fall-2001/basiccat.ps.gz [7]:http://www.maths.gla.ac.uk/~tl/ct/ [8]:http://cheng.staff.shef.ac.uk/catnotes/categorynotes-cheng.pdf [9]:http://www.andrew.cmu.edu/course/80-413-713/notes/ [10]:http://www.dcs.ed.ac.uk/home/dt/CT/ [11]: http://www.mathematik.tu-darmstadt.de/~streicher/CTCL.pdf [12]: http://katmat.math.uni-bremen.de/acc/ [13]:http://en.wikibooks.org/wiki/Haskell/Category_theory [14]:http://blog.sigfpe.com [15]:http://comonad.com/reader/ [16]:http://www.haskell.org/sitewiki/images/8/85/TMR-Issue13.pdf [17]: http://www.cs.le.ac.uk/people/akurz/books.html [18]: http://tac.mta.ca/tac/reprints/articles/17/tr17.pdf [19]: http://ocw.mit.edu/courses/mathematics/18-s996-category-theory-for-scientists-spring-2013/textbook/MIT18_S996S13_textbook.pdf [20]: http://repository.cmu.edu/cgi/viewcontent.cgi?article=2846&context=compsci [21]: https://mathoverflow.net/users/2841/martin-brandenburg