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.

To find out which biotech companies are the biggest (and arguably most successful) on Earth, check out the slideshow below. And if you're looking for other investing ideas that could give you big returns, we've got you covered. The Motley Fool's free report, "3 Stocks That Will Help You Retire Rich," names stocks that could help you build long-term wealth and retire well, along with some winning wealth-building strategies that every investor should be aware of. Click here now to get your free copy.