  The aim of these lecture notes is to familiarize graduate students and
beginning postgraduates with the basic ideas of linear cosmological
perturbation theory and of structure formation scenarios. We present both the
Newtonian and the general relativistic approaches, derive the key equations and
then apply them to a number of characteristic cases. The gauge problem in
cosmology and ways to circumvent it are also discussed. We outline the basic
framework of the baryonic and the non-baryonic structure formation scenarios
and point out their strengths and shortcomings. Fundamental concepts, such as
the Jeans length, Silk damping and collisionless dissipation, are highlighted
and the underlying mathematics are presented in a simple and straightforward
manner.
