In this thesis I present an observational study of the evolution of Cataclysmic Variables (CVs). Disrupted magnetic braking has been the standard paradigm of CV evolution for the past twenty years. Unfortunately, some of its predictions are in strong disagreement with the observations. In recent years, a number of additions/alternatives to the standard model have been proposed. Yet, none have been able to explain all of the features observed in the currently known CV population. The work presented in this thesis is based mainly on a large-scale search for CVs. The primary aim of this project is to resolve the disagreement between theory and observations by eliminating the observational biases of the present CV sample. Here I use two complementary approaches to search for CVs: (1) from the spectroscopic appearance in the Hamburg Quasar Survey (HQS) and (2) by using a combination of X-ray emission and multi-colour selection criteria in the RSAT and 2MASS archival data. So far, we have discovered 52 new CVs in the HQS and 11 new CVs (the majority of them magnetic) and one pre-CV in the ROSAT/2MASS. Follow-up observations of two newly discovered HQS CVs, 1RXS J062518.2+733433 and HS 2331+3905, resulted in the classification of the first as an Intermediate Polar, with P_orb = 283.0 min and P_spin = 19.8 min, and the second as a short orbital period system, P_orb = 81.0 min, harboring a white dwarf pulsator. In addition, we found that the dominant ~ 2.3 h radial velocity variation of HS 2331+3905, does not correspond to the orbital period of the system, contrary to all other CVs. Despite its novel selection criterion, the HQS does not provide many short-period CVs - even though tests with the known CVs included in the survey have shown that it is very sensitive to those objects. The biggest surprise in the new HQS CV sample is the discovery of many new SW Sex stars. The clustering of SW Sex stars in the 3-4 h period range is probably an important feature in the evolution of CVs that we currently do not understand at all. To improve our chances of understanding what is going on in that period range, we need accurate system parameters for these stars, which is difficult mainly because of their defining characteristics. I have used HST data of one of the sporadic low states of the SW Sex star, DW UMa, to derive its systems parameters. The success of this study is the first step towards the otherwise impossible task of compiling reliable system parameters for the SW Sex stars.