The IT Band is often the "scapegoat" of knee, thigh or hip pain. I often hear people are stretching or rolling their IT band in order to alleviate such pain, and often to little avail.
The IT or iliotibial band is a band of connective tissue stretching from the hip to just below the outside of the hip as illustrated in the picture above and has three distinct layers - superficial, intermediate and deep - different muscles connect to different layers. The IT band itself has no ability to contract, i.e. it has no contractile tissue. This means that the band itself is not the root cause of tightness or pain, rather the muscles that attach to it are what cause the IT band to be tight.
If you want to relieve the IT band the correct way to do so is by stretching the MUSCLES that are tight and causing the tension. As you can see in the illustration there are many possible causes (muscles) that are affecting your IT band.