  The stellar content of the nearby SB(s)m galaxy NGC 55 is investigated using
images covering the visible and near-infrared wavelength regions. A
well-defined plume, which stellar evolution models suggest contains stars with
masses near the RSG - AGB transition, is detected in CMDs of the disk, and it
is concluded that star formation in the thin disk of NGC 55 has ocurred at a
significant rate for at least the past 0.1 - 0.2 Gyr. The disk also contains a
large population of old (log(t_yr) ~ 10) stars, and it is argued that a stable
disk has been in place in NGC 55 for a significant fraction of the age of the
Universe. At projected distances in excess of 2 kpc off of the disk plane the
brightest AGB stars have ages 10(+3)(-2) Gyr. Thus, despite indications that
dust and gas are present in the envelope surrounding the NGC 55 disk, the AGB
content suggests that recently formed stars do not occur in large numbers in
the extraplanar region. The mean metallicity of extraplanar RGB stars is in
excellent agreement with that measured in the extraplanar HII regions EHR 1 and
2, suggesting that the age-metallicity relation in this part of NGC 55 has been
flat for at least a few Gyr. Finally, the RGB-tip occurs near i' = 23.1 in the
extraplanar region, and a distance modulus of 26.5 is computed from this
feature.

Astrophysics