These notes discuss two aspects of the physics of atomic Bose-Einstein condensates:
optical properties and spinor condensates. The first topic includes light scattering
experiments which probe the excitations of a condensate in both the free-particle
and phonon regime. At higher light intensity, a new form of superradiance and
phase-coherent matter wave amplification were observed. We also discuss properties
of spinor condensates and describe studies of ground-state spin domain structures
and dynamical studies which revealed metastable excited states and quantum tunneling.