The contents of this book correspond to Sessions VII and VIII of the International Workshop on Instabilities and Nonequilibrium Structures which took place in Vina del Mar, Chile, in December 1997 and December 1999, respectively. Part I is devoted to self-contained courses. Three courses are related to new developments in Bose-Einstein condensation: the first one by Robert Graham studies the classical dynamics of excitations of Bose condensates in anisotropic traps, the second by Marc Etienne Brachet refers to the bifurcations arising in attractive Bose-Einstein condensates and superfluid...