  Although the theory of cataclysmic variable (CV) evolution is able to explain
several observational aspects, strong discrepancies have existed for decades
between observations and theoretical predictions of the orbital period
distribution, the location of the minimum period, and the space density of CVs.
Moreover, it has been shown in the last decade that the average white dwarf
(WD) mass observed in CVs is significantly higher than the average mass in
single WDs or in detached progenitors of CVs, and that there is an absence of
helium-core WDs in CVs which is not observed in their immediate detached
progenitors. This highly motivated us to revise the theory of CV formation and
evolution. A new empirical model for angular momentum loss in CVs was developed
in order to explain the high average WD mass observed and the absence of
systems with helium-core WDs. This model seems to help, at the same time, with
all of the above mentioned disagreements between theory and observations.
Moreover, it also provides us with a very likely explanation for the existence
of low-mass WDs without a companion. Here we will review the standard model for
CV evolution and the disagreements that have existed for decades between
simulations and observations with their possible solutions and/or improvements.
We will also summarize the recently confirmed disagreement related to the
average WD mass and the fraction of helium-core WDs among CVs, as well as the
development of an empirical model that allows us to solve all the
disagreements, discussing the physics that could be involved.
