Warnaar has made several groundbreaking contributions to the fields of solvable lattice models, special functions, q-series and algebraic combinatorics. He is the discoverer of the first solvable two-dimensional lattice model in the presence of a symmetry breaking magnetic field and a pioneer in the theory of elliptic hypergeometric series. Together with A Schilling he discovered the generalised Kostka-Foulkes polynomials and supernomial coefficients, and in joint work with G Andrews and Schilling he provided the first examples of Rogers-Ramanujan identities for the Lie algebra A 2.