In recent years it we have learned that stars need not remain at the radius 
at which they were born their entire lives.  Instead, interaction with 
transient spirals at their corotation resonances can give rise to a large 
amount of migration while retaining nearly circular orbits of stars. 
Migration has a huge impact on the properties of disk galaxies. 
In this talk I will review the spiral driven migration and present evidence 
for it in the Milky Way and in external galaxies.