  We summarize observational results on the stellar population and star
formation history of the Scorpius-Centaurus OB Association (Sco OB2), the
nearest region of recent massive star formation. It consists of three
subgroups, Upper Scorpius (US), Upper Centaurus-Lupus (UCL), and Lower
Centaurus-Crux (LCC) which have ages of about 5, 17, and 16 Myr. In Upper
Scorpius, numerous studies have recently revealed hundreds of low-mass
association members, including dozens of brown dwarfs. The empirical mass
function could be established over the full stellar mass range from 0.1 M_sun
up to 20 M_sun, and was found to be consistent with recent determinations of
the field initial mass function. A narrow range of ages around 5 Myr was found
for the low-mass stars, the same age as had previously (and independently) been
derived for the high-mass members. This supports earlier indications that the
star formation process in US was triggered, and agrees with previous
conjectures that the triggering event was a supernova- and wind-driven
shock-wave originating from the nearby UCL group. In the older UCL and LCC
regions, large numbers of low-mass members have recently been identified among
X-ray and proper-motion selected candidates. In both subgroups, low-mass
members have also been serendipitously discovered through investigations of
X-ray sources in the vicinity of better known regions (primarily the Lupus and
TW Hya associations). While both subgroups appear to have mean ages of ~16 Myr,
they both show signs of having substructure. Their star-formation histories may
be more complex than that of the younger, more compact US group. ... (abstract
abbreviated; see paper for full abstract).
