Nigel Weiss was renowned for his work in the theory of convection, for developing appropriate numerical techniques, and for pioneering their use in precise numerical experiments in order to gain a qualitative and comprehensive understanding of the behaviour of complicated nonlinear systems. Among many notable achievements in this field, he was instrumental in the identification of a period-doubling route to chaos in a system of partial differential equations describing doubly-diffusive convection. He made wide-ranging studies of the magnetoconvective processes occurring in the Sun and similar stars. In early work of lasting influence, he analysed the process of magnetic flux expulsion and the mechanism of concentration of the magnetic field into ropes from which fluid motion is excluded. Later, he initiated a programme of research in the field of nonlinear compressible convection, an important step towards realistic modelling of stellar convection zones.