Pranayama (Chinese Qi Gong, Tibetan Cha Lung) is a series of practices focused on the breath. These practices have become increasingly popular over the past decade or two, but unfortunately most people are doing the practices completely wrong. When done right, Pranayama can heal serious illness without any other method complimenting it. Because these practices are so potent, when done wrongly, the same practices can also be the cause of serious illness, or even death.
Like any other yoga practice, practitioners should start with little in terms of time and intensity and then work from there according to the individual capability and progress.
Perhaps the most significant contribution to the field in terms of written text is the B. K. S. Iyengar’s Light on Pranayama which can be accessed for free in pdf format. Read it here.