  The Lagoon Nebula is an HII region in the Sagittarius Arm, about 1.3 kpc
away, associated with the young (1-3 Myr) open cluster NGC 6530, which contains
several O stars and several dozen B stars. Lower-mass cluster members, detected
by X-ray and H-alpha emission, and by near-IR excess, number more than a
thousand. Myr-old star formation is traced by the optically-visible HII region
and cluster; observations of infrared and submillimetre-wave emission, and of
optical emission features, indicate ongoing star formation in several locations
across the Lagoon. The most prominent of these are the Hourglass Nebula and
M8E. Submillimetre-wave observations also reveal many clumps of dense molecular
gas, which may form the next generation of stars. The complex structure of the
region has been shaped by the interaction of the underlying molecular gas with
multiple massive stars and episodes of star formation. NGC 6530 is the oldest
component, with the newest stars found embedded in the molecular gas behind the
cluster and at its southern rim. A degree to the east of the Lagoon, Simeis 188
is a complex of emission and reflection nebulae, including the bright-rimmed
cloud NGC 6559; the presence of H-alpha emission stars suggests ongoing star
formation.
