  This text aims to give a pedagogical introduction into the main concepts of
the theory of structure formation in the universe. The text is suited for
graduate students of astronomy with a moderate background in general
relativity. A special focus is laid on deriving the results formally from first
principles. In the first chapter we introduce the homogeneous and isotropic
universe defining the framework for the theory of structure formation, which is
discussed in the three following chapters. In the second chapter we describe
the theory in the Newtonian framework and in the third chapter for the general
relativistic case. The final chapter discusses the generation of perturbations
in the very early universe for the simplest models of inflation.
