Upcoming surveys such as HSC, DES, and eventually EUCLID and LSST, have the potential to make gravitational lensing a decisive tool in probing the universe. To exploit these new measurements, systematic errors will have to be understood at the ~1% level. The intrinsic alignment (IA) of source galaxies constitutes a significant systematic uncertainty. After providing a brief description of IA, I will discuss our efforts to understand and control IA from both theoretical and observational perspectives, emphasizing the context of galaxy-galaxy weak lensing. In addition to its role as a contaminant, IA can teach us about a variety of physical processes such as galaxy formation and primordial gravitational waves.