This volume presents an account of the current state of algebraic-theoretic methods as applied to linear and nonlinear multidimensional equations of mathematical and theoretical physics. Equations are considered that are invariant under Euclid, Galilei, Schrodinger, Poincare, conformal, and some other Lie groups, with special emphasis being given to the construction of wide classes of exact solutions of concrete nonlinear partial differential equations, such as d'Alembert, Liouville, Monge-Ampere, Hamilton-Jacobi, eikonal, Schrodinger, Navier-Stokes, gas dynamics, Dirac, Maxwell-Dirac,...