Abstract
A geometrical setting in terms of jet manifolds is developed for time-dependent non-holonomic Lagrangian systems. An almost product structure on the evolution space is constructed in such a way that the constrained dynamics is obtained by projection of the free dynamics. A constrained Poincaré - Cartan 2-form is defined. If the non-holonomic system is singular, a constraint algorithm is constructed. Special attention is devoted to Caplygin systems and a reduction theorem is proved.