  We present images and initial results from our extensive Spitzer Space
Telescope imaging survey of the W5 H II region with the Infrared Array Camera
(IRAC) and Multiband Imaging Photometer for Spitzer (MIPS). We detect dense
clusters of stars, centered on the O stars: HD 18326, BD +60 586, HD 17505 and
HD 17520. At 24 microns substantial extended emission is visible, presumably
from heated dust grains that survive in the strongly ionizing environment of
the H {\sc ii} region. With photometry of more than 18000 point sources, we
analyze the clustering properties of objects classified as young stars by their
IR spectral energy distributions (a total of 2064 sources) across the region
using a minimal-spanning-tree algorithm. We find ~40--70% of infrared excess
sources belong to clusters with >10 members. We find that within the evacuated
cavities of the H II regions that make up W5, the ratio of Class II to Class I
sources is ~7 times higher than for objects coincident with molecular gas as
traced by 12CO emission and near-IR extinction maps. We attribute this contrast
to an age difference between the two locations, and postulate that at least two
distinct generations of star formation are visible across W5. Our preliminary
analysis shows that triggering is a plausible mechanism to explain the multiple
generations of star formation in W5, and merits further investigation.
