This chapter is entirely devoted to Lagrange’s VWL. In the first part the first introduction of the law of Lagrange is reported, which has a wording similar to that of Bernoulli. Lagrange calls his VWL and Bernoulli’s the principle of virtual velocities. In the central part the wordings of VWL in the two editions of the Mécanique analytique in terms of virtual displacements (following a foundational route) and the Théorie des fonctions analytique in terms of virtual velocity (following a reductionist route) are presented. In the final part an overview of D’Alembert’s mechanics is presented aimed at an understanding of the extensibility of VWLs to dynamics.