In the past decades, many complex systems, either natural, social, or artificial, have been modeled as networks of coupled dynamical systems, with the links describing interactions among couples of units. However, recent evidence shows that various systems are characterized by many-body, group interactions that cannot be captured by a network description. In the last few years, a vast literature aimed at understanding how these higher-order interactions influence the collective behavior of coupled systems has grown. In this talk, I will show how to develop a theory for synchronization of coupled nonlinear oscillators in presence of higher-order interactions. I will introduce a mathematical formalism to describe coupled dynamics in a general framework, and I will show how it can be used to derive the necessary conditions for the emergence of a synchronous state.