I will present an overview of the GHOSTS survey, the largest study to date of the resolved stellar populations in the outskirts of disk galaxies. The sample consists of 14 disk galaxies within 17 Mpc, whose outer disks and halos are imaged with the Hubble Space Telescope. Iwill explore the benefits of using resolved stellar populations, and discuss the F606W and F814W photometry. We use artificial star tests to assess completeness and use overlapping regions to estimate photometric uncertainties. The median depth of the survey at 50% completeness is 2.7 mag below the tip of the red giant branch (TRGB). We comprehensively explore and parameterize contamination from unresolved background galaxies and foreground stars using archival fields.
Tho GHOSTS Survey has yielded results on the color, extent, mass and shape of the stellar haloes, evidence of primordial accretion. As recent result I will discuss the Pinwheel galaxy M101 and implications for galaxy formation models.