Recent theoretical work suggests that it may be common for stars in the disks of spiral galaxies to migrate radially across significant distances in the disk. Such migrations are a result of spiral corotation resonance scattering and move the guiding centers of the stars while preserving the circularities of their orbits. Migration can therefore efficiently mix stars in all parts of the disk. Therefore, if migration does indeed occur in real disks, it requires that disks be thought of as fully inter-connected structures with a common history rather then a set of autonomous regions. In the extreme, radial migration allows the evolution of the innermost regions to contribute significantly to the outermost parts of the disk. I will discuss the results from idealized N-body/SPH simulations of disk formation and evolution, emphasizing the observational consequences of stellar migration on the solar neighborhood, the thick and thin disks of the Galaxy, as well as external disks.