Recent advancement in design and fabrication of multimode optical fibers, for example supporting stable propagation of orbital angular momentum modes or optical activity modes, have led to new advances and opportunities within nonlinear interactions. The nonlinear effects have applications that range from fiber lasers to optical communication using classical light, as well as quantum states. In the lecture, focus will be given to Raman scattering and four-wave mixing in multimode fibers supporting conventional linearly polarized modes and, more exotic modes as orbital angular momentum or optical activity modes. Examples of applications include amplification of structured light and generation and processing of quantum states.