This chapter serves as a window to Lagrangian mechanics. Generalized coordinates for a constrained mechanical system are defined as a means for specifying a particular configuration in the configuration space of the system. Power and generalized forces are considered next. Lagrange’s equations are derived for a constrained system of particles on the basis of Newton’s second law. The Lagrangian function is defined based on the potential energy of conservative forces. Finally, Lagrange’s equations are written in terms of the Lagrangian function.