The use of geometric methods in classical mechanics has proven to be a fruitful exercise, with the results being of wide application to physics and engineering. Here Professor Marsden concentrates on these geometric aspects, and especially on symmetry techniques. The main points he covers are: the stability of relative equilibria, which is analyzed using the block diagonalization technique, geometric phases, studies using the reduction and reconstruction technique, and bifurcation of relative equilibria and chaos in mechanical systems.