These proceedings contain the refereed papers and posters presented at the S- ond International Conference on the Theory of Information Retrieval (ICTIR 2009), held at Microsoft Research in Cambridge, UK, September 10-11, 2009. This biennial international conference provides an opportunity for the p- sentation of the latest work describing theoretical advances in the ?eld of inf- mation retrieval (IR). The ?rst ICTIR was held in Budapest in October 2007, organizedby Keith van Rijsbergen, Sa ndor Dominich, S andor Daran yi, and F- enc Kiss. ICTIR was brought about by the growing interest in...