After dealing with the linear instabilities in the previous chapter we now shift the attention to the nonlinear dynamics of waves in two-dimensional electronic systems, with a focus on the hydrodynamics of nonlinear waves in graphene. The chapter begins by discussing nonlinear hydrodynamic models and explores the conditions under which finite-amplitude waves develop. Both small and finite-amplitude nonlinear waves are studied using equations such as the dissipative Kadomtsev—Petviashvili equation and the nonlinear Schrödinger equation. The chapter then addresses the modulational instability that arises in graphene, providing insights into the nonlinear interactions between charge carriers and plasmons. Numerical simulations are used to validate the theoretical predictions, showing the emergence of solitonic solutions and complex wave interactions. These results are crucial for understanding the nonlinear behaviour of 2D electronic systems and have implications for the development of nonlinear photonic and electronic devices based on graphene and similar materials.