  We discuss three aspects of post-AGB (PAGB) stars in old populations. (1) HST
photometry of the nucleus of the planetary nebula (PN) K 648 in the globular
cluster (GC) M15 implies a mass of 0.60 Msun, in contrast to the mean masses of
white dwarfs in GCs of ~0.5 Msun. This suggests that K 648 is descended from a
merged binary, and we infer that single Pop II stars do not produce visible
PNe. (2) Yellow PAGB stars are the visually brightest stars in old populations
(Mv ~ -3.3) and are easily recognizable because of their large Balmer jumps;
thus they show great promise as a Pop II standard candle. Two yellow PAGB stars
in the GC NGC 5986 have the same V magnitudes to within +/-0.05 mag, supporting
an expected narrow luminosity function. (3) Using CCD photometry and a u filter
lying below the Balmer jump, we have detected yellow PAGB stars in the halo of
M31 and in its dwarf elliptical companion NGC 205. With the Milky Way zero
point, we reproduce the Cepheid distance to M31, and find that NGC 205 is ~100
kpc further away than M31. The star counts imply a yellow PAGB lifetime of
about 25,000 yr, and their luminosities imply masses near 0.53 Msun.
