  Modern cosmology has created a tight link between particle physics / field
theory and a wealth of new observational data on the structure of the Universe.
These lecture notes focus on some of the most important aspects concerning the
connection between theory and observations. The lectures begin with an overview
of some recent progress and problems in inflationary cosmology. In particular,
a pedagogical discussion of the theory of reheating is presented. The second
topic is a survey of the theory of cosmological perturbations, the cornerstone
of modern cosmology. The focus is on the gauge-invariant classical and quantum
theory of fluctuations. The third topic concerns the role of topological
defects in cosmology. Reviews of the cosmic string theory of galaxy formation
and of defect-mediated GUT and electroweak baryogenesis are given.
