Few musical arenas are as competitive as hip hop. Album sales, video budgets, cribs, cars, marquee features—the measuring sticks are endless. The mixtape is both one of the most important and one of the most intangible, a space where artists hustle to top each other while embracing their fans without a middleman in the way. The tracks borrow—and sometimes take over—existing beats; established and upcoming producers show off their looser work and aces they've kept up their sleeve until the right moment. Mixtapes don't tend to find radio play, but they converse with each other in a meaningful, lasting way that shapes trends and builds careers. And they're usually free! 

Here are 10 of the best mixtapes from the last decade.