This chapter discusses the importance of efficient wave propagation models for generating boundary conditions for CFD models of wave-structure interaction or as elements of hybrid models. We give a brief review of fully nonlinear wave models based on potential flow theory (FNPT), which are the main candidates for such applications. We then suggest a Lagrangian wave model as an alternative to classical FNPT models. We present a mathematical and numerical formulation of the model, its validation and application to propagation of steep wave groups and to wave groups on sheared currents.