SelbstständigkeitserklärungHiermit erkläre ich, dass ich die vorliegende Dissertation selbsständig und nur unter Verwendung der angegebenen Literatur und Hilfsmittel angefertig habe.i ii Acknowledgements I wish to thank my supervisor Klaus Mohnke, who introduced me to the field of symplectic and contact geometry. The discussions with him were at the same time inspiring and encouraging. Without him insisting on clear explanations, some parts of this thesis would never have been written.