  We review the properties of the currently known CV population from an
accountants point of view. In particular, it is examined to what extent
different selection mechanisms (variability, X-ray emission, colours,
spectroscopic properties) affect the observed CV orbital period distribution.
Large-scale surveys provide homogeneously selected CV samples, for which
observational biases can in principle be modelled. Such samples will eventually
provide the essential observational input for an improved understanding of CV
evolution, and we highlight the impact of several completed and on-going
surveys.
