  We construct a complete, semi-empirical donor sequence for CVs with orbital
periods less than 6 hrs. All key physical and photometric parameters of CV
secondaries (along with their spectral types) are given as a function of P_orb
along this sequence. The main observational basis for our donor sequence is an
empirical mass-radius relation for CV secondaries. We present an optimal
estimate for this relation that ensures consistency with the observed locations
of the period gap and the period minimum. We also present new determinations of
these periods, finding P_{gap, upper edge} = 3.18 +/- 0.04 hr, P_{gap, lower
edge} = 2.15 +/- 0.03 hr and P_{min} = 76.2 +/- 1.0 min. We then test the donor
sequence by comparing observed and predicted spectral types (SpTs) as a
function of orbital period. To this end, we update the SpT compilation of
Beuermann et al. and show explicitly that CV donors have later SpTs than main
sequence (MS) stars at all orbital periods. The semi-empirical donor sequence
matches the observed SpTs very well, implying that the empirical M2-R2 relation
predicts just the right amount of radius expansion. We finally apply the donor
sequence to the problem of distance estimation. Based on a sample of 22 CVs
with trigonometric parallaxes, we show that the donor sequence correctly traces
the envelope of the observed M_{JHK}-P_{orb} distribution. Thus robust lower
limits on distances can be obtained from single-epoch infrared observations.
