Ramanujan’s lost notebook - a treasure - was unearthed by G. E. Andrews in 1976. This notebook contains a number of beautiful identities involving theta series. One of the identities in this class is the reciprocity theorem of Ramanujan. In the recent past a number of authors have contributed to the proofs of the reciprocity theorem and to its generalizations and applications. In this talk I shall give an account of all those ramifications of this well-known identity.