  A method, based on the disc instability model, for testing the thermal
stability of Cataclysmic Variables (CVs), is presented. It is shown that the
border line between thermal stability and instability is crossed during some
nova outbursts and decays, however it is not clear whether this is the general
behaviour. We suggest two new evolutionary scenarios for short orbital period
CVs. One of them is the analogy for the 'modified hibernation scenario' and the
other is an extension of the ideas of Mukai and Naylor (1993) for long orbital
period CVs. We conclude that the observations have not favoured one of the two
models. Finally, we speculate the existence of a new type of nova - an AM CVn
like nova.
