In this lecture the family of wavefunction based ab-inito methods will be presented. A comparison of accuracy, efficientcy and availability of methods in comparison to the common density functional theory approaches will be made.

Extensive benchmark studies will be presented in order to enable the students of the course to assess the quality of theoretical methods that are commonly used for the description of molecular and supramolecular systems.

The framework for the calculation of molecular properties will be discussed and the capability of current computer codes for the application in physics and chemistry is outlined.

Throughout the course examples of recent applications will be used to underline the impact that theoretical investigations can have in different fields of modern science.