Biotech investing is known for its volatility. Week in and week out, biotechs crash and burn on disappointing clinical results, safety concerns, or one of a wide variety of other reasons. Some biotechs, though, don't just succeed on a small scale; they hit the big time.

Which biotech companies are the biggest on the planet? It depends on how you define "big," of course. In the slideshow below, we answer this question by determining which biotechs have the largest market caps. And we take a look at other key metrics, like revenue and earnings -- plus examine the secrets to each company's success.