I find it hard to believe the MiG-21 design is almost as old as I am and is still serving as a front-line fighter in several air forces around the world. I’m still pretty active, but no longer a “front-line fighter” by any stretch of the imagination. Since the end of WWII, in almost any conflict involving Western air forces, the adversary has been a Mikoyan-Gurevich designed aircraft: in many instances, the MiG-21 Fishbed.
In Mikoyan-Gurevich MiG-21, Alexander Mladenov thoroughly covers the MiG-21 from its early development to its role in several conflicts around the world. His descriptions are often technical, but very readable nonetheless. The chapter titles give a good idea what is discussed: