  We present our recent results on the properties of the outskirts of disk
galaxies. In particular, we focus on spiral galaxies with stellar disk
truncations in their radial surface brightness profiles. Using SDSS, UDF and
GOODS data we show how the position of the break (i.e., a direct estimator of
the size of the stellar disk) evolves with time since z~1. Our findings agree
with an evolution on the radial position of the break by a factor of 1.3+/-0.1
in the last 8 Gyr for galaxies with similar stellar masses. We also present
radial color gradients and how they evolve with time. At all redshift we find a
radial inside-out bluing reaching a minimum at the position of the break
radius, this minimum is followed by a reddening outwards. Our results constrain
several galaxy disk formation models and favour a scenario where stars are
formed inside the break radius and are relocated in the outskirts of galaxies
through secular processes.
