  Ramanujan influenced many areas of mathematics, but his work on q-series, on
the growth of coefficients of modular forms, and on mock modular forms stands
out for its depth and breadth of applications. I will give a brief overview of
how this part of Ramanujan's work has influenced physics with an emphasis on
applications to string theory, counting of black hole states and moonshine.
This paper contains the material from my presentation at the meeting
celebrating the centenary of Ramanujan's election as FRS and adds some
additional material on black hole entropy and the AdS/CFT correspondence.
