  The shape of the main arc formed by the Canis Major clouds has been suggested
to result from a supernova explosion possibly triggering the recent star
formation activity. The presence of dozens of OB stars and reflection nebulae
forms the CMa OB1/R1 associations. More than a hundred emission line stars are
found in this region, including the famous Z CMa, a binary system containing a
Herbig Be star and a FUor companion. Several embedded infrared clusters with
different ages are associated with the CMa clouds. The main characteristics of
the region in terms of cloud structure, stellar content, age of associated
young clusters, distance, and X-ray emission are presented in this chapter.
Some of the arguments in favor and against the hypothesis of induced star
formation are discussed in the last section.
