  We present VRI photometry of 320,917 stars with 11 < R < 18 throughout the
lambda Orionis star-forming region. We statistically remove the field stars and
identify a representative PMS population throughout the interior of the
molecular ring. The spatial distribution of this population shows a
concentration of PMS stars around lambda Ori and in front of the B35 dark
cloud. Few PMS stars are found outside these pockets of high stellar density,
suggesting that star formation was concentrated in an elongated cloud extending
from B35 through lambda Ori to the B30 cloud. We find a lower limit for the
global stellar mass of about 500 Mo. We find that the global ratio of low- to
high-mass stars is similar to that predicted by the field initial mass
function, but this ratio varies strongly as a function of position in the
star-forming region. Locally, the star-formation process does not produce a
universal initial mass function. We construct a history of the star-forming
complex. This history incorporates a recent supernova to explain the
distribution of stars and gas today.
