CV and LMXB Population Synthesis

I discuss population synthesis methods in the context of low-mass compact binaries. Two examples, both constraining the largely unknown strength of orbital angular momentum losses, illustrate the power and problems of such studies. For CVs, the ``standard'' disrupted magnetic braking model predicts that systems below the period gap are on average older than systems above the gap. The corresponding difference in the space velocity dispersion is testable by observations, independent of brightness-dependent selection effects. For LMXBs, the fraction of transients among short-period neutron star systems turns out to be an important diagnostic quantity constraining not only the angular momentum loss rate but also the kick velocity imparted to the neutron star at birth and the common envelope efficiency. Small kicks (less than 100 km/s), low efficiencies and weak magnetic braking are strongly favoured.