Book excerpt: The aim of these lecture notes is to provide a self-contained exposition of several fascinating formulas discovered by Srinivasa Ramanujan. Two central results in these notes are: (1) the evaluation of the RogersOCoRamanujan continued fraction OCo a result that convinced G H Hardy that Ramanujan was a OC mathematician of the highest classOCO, and (2) what G. H. Hardy called Ramanujan''s OC Most Beautiful IdentityOCO. This book covers a range of related results, such as several proofs of the famous RogersOCoRamanujan identities and a detailed account of Ramanujan''s congruences. It also covers a range of techniques in q-series."