Nonlinear optics in complex nanostructures is an exciting and rapidly evolving field that holds immense potential for advancements, with implications for fundamental scientific understanding and a wide range of practical applications across the electromagnetic spectrum, from visible, infrared to THz and microwave frequencies. This session will cover a wide range of topics related to nonlinear optical phenomena in intricate nanoscale systems. The coverage includes, but is not limited to, the following areas: nonlinear metasurfaces/metamaterials, nonlinear effects in quantum optics, low-dimensional materials for nonlinear optics, nonlinear plasmonics, ultrafast nonlinear optics and nonlinear topological photonics.