The idea of "earning money while you sleep" sounds like a pipe dream, but plenty of people do it. It's what's called passive income—money you earn on a regular basis that requires little to no effort to receive it. If Mick Jagger is still earning royalties on "Gimme Shelter," a track that debuted in 1969, every time it plays on TV, that's passive income. Whether the IRS taxes it as passive income is another story, but in the realm of earning money while you sleep, it still fits the bill. Those checks are just rollin' in for Jagger.
So what if you don't have a record deal or if you're not the next Monica Geller? There are actually plenty of ways to earn money while you sleep. In fact, Tim Ferriss, author of The Four-Hour Work Week, has gained much of his notoriety—and wealth—by promoting and using different passive income streams. Read on to learn about some of the most accessible ones.

Affiliate marketing is a super-accessible way to earn money. Anyone can do it. The way it works is that you build a website or blog (with a strong following!) on any topic of your choice, and you refer your readers to products from retail partners. Maybe it's a book you just read and loved, or perhaps it's the shoes you wore in your latest Look of the Day blog post. Every time one of your readers makes a purchase from one of your retail partners, you get a small portion of the sale (a pre-determined percentage, often between 3 and 15 percent). Your reader doesn't even have to purchase the exact product you referred: So long as he or she makes a purchase within your allotted "cookie window" (often 30 days), you'll get paid. If he or she leaves the site and comes back a week later and then buys something, you'll still get paid. So on that note, in a very real way, you could actually be sleeping while your reader buys something you suggested, and you'd get a check for it.
There are a number of companies that faciliate relationships between affiliate pubishers and retailers. Some of the big ones are LinkShare, CJ Affiliate, eBay Enterprise, and ShareASale. They'll set you up with tracking links so you and your retail partners can see what sales you're driving.
Sound like something you're interested in? Who What Wear's new eBook will show you how to get it done in 90 days.

Peer-to-peer lending is an interesting and relatively new industry. A variety of online lending marketplaces (like LendingClub, Propser, and Harmoney) match lenders (who invest in consumer loans) with borrowers, consumers who may have had a hard time getting a traditional bank loan or other form of credit. Like making any investment, there is risk involved, but as a lender, you have the opportunity to earn great returns as the loan is paid back with interest. There are also peer-to-peer lending marketplaces for student loans (SoFi) and small businesses (FundingCircle). In any case, all you have to do is fork over some cash temporarily, sit back, sleep, and watch it grow.