S4G is the ultimate survey of the distribution of stellar structure in the nearby universe using IRAC's 3.6 and 4.5 micron channels during the Warm Mission. S4G will survey the stellar mass distribution in 2300 nearby (d<40Mpc) galaxies to create an unprecedented data set for studies of structure formation during galaxy evolution. These observations will provide answers to some of the most fundamental questions of our field: how are outer disks and halos formed? how do galaxy interactions affect the formation and evolution of galactic structures? which structural parameters govern internal galaxy evolution? Our large unbiased sample of all Hubble types ranging from dwarfs to spirals to ellipticals will allow for such structural studies, not only as a of stellar mass, but also as a function of environment, and the output of such an immense survey will serve as a vital testbed for cosmological simulations predicting the mass properties of present-day galaxies.