The present thesis reviews my scientific works on disordered systems from 1995 until today. They can be roughly categorized into three main classes: (1) non-interacting disordered systems, (2) the two-interacting particle problem, and (3) the interplay of disorder and many-particle interaction. A (4)th chapter is concerned with the implementation of the numerical algorithms. The structure of the thesis reflects this division. The reprints have been added at the end of these main divisions according to their context. For the convenience of the reader, I have ordered them in each chapter alphabetically according to the names of the authors. Furthermore, in each citation of my work, the starting page number in the thesis is given, e.g, Ref.\ \cite{EPR97} refers to a paper of Eckle, Punnoose and myself and can be found on page \pageref{EPR97}. Citations which do not refer to my work are numbered and are ordered in the bibliography according to the names of the authors.

The present thesis reviews my scientific works on disordered systems from 1995 until today. They can be roughly categorized into three main classes: (1) non-interacting disordered systems, (2) the two-interacting particle problem, and (3) the interplay of disorder and many-particle interaction. A (4)th chapter is concerned with the implementation of the numerical algorithms. The structure of the thesis reflects this division. The reprints have been added at the end of these main divisions according to their context. For the convenience of the reader, I have ordered them in each chapter alphabetically according to the names of the authors. Furthermore, in each citation of my work, the starting page number in the thesis is given, e.g, Ref.\ \cite{EPR97} refers to a paper of Eckle, Punnoose and myself and can be found on page \pageref{EPR97}. Citations which do not refer to my work are numbered and are ordered in the bibliography according to the names of the authors.