"Any track, any time, anywhere. And it's free!" That's the mantra of one of Europe's most popular — and praised — music streaming services, the Sweden-based Spotify. And now, the service, which has 10 million users across Europe, is coming stateside, though no specific launch date has been set. Spotify allows users to stream almost any widely released song online for free, and American music fans have been rabid for its debut in the U.S.—which has been almost two years in the making. Here, a brief guide:

What makes Spotify so great?
For starters, there's the sheer number of songs offered. "When you get the urge to listen to a particular song, it's there — and you don't need to jump through any hoops to get it," says Kat Hannaford at Gizmodo. The European version of Spotify has been diligent in securing permission from the major record labels, meaning all listening is legal. You can listen to whole albums, individual songs, or organize playlists — which can be shared online with friends who can add to the playlist themselves. Spotify will also import your existing music library, "so you theoretically never have to listen to iTunes again," says Jared Newman at TIME.

And it's free?
Yup. It doesn't cost anything to download or use Spotify, though there are some restrictions. You can listen to 10 hours of music per month, and five listens per track for free. For $5 a month, those restrictions are lifted, and you get unlimited online streaming. Make it $10 a month, and you can access to Spotify on mobile devices, too.

How do I get it?
The announcement on Spotify's website only says that the service is coming to the U.S. "soon," though "sources" at Billboard anticipate that its launch is likely to come next week. Typically, you have to be invited to join Spotify. But the company's website is currently allowing prospective users to sign up for an invitation.

Why has it taken so long to get here?
Plans for Spotify to enter the American market date back to July 2009. The company aims to offer the same extensive song library it makes available in Europe, and "it's no secret" that record labels here haven't been as generous licensing their content, says Britain's Guardian. But after securing a $100 million investment in June, it appeared that the company would have the resources to close deals with the labels.

Will it be a success?
Spotify's free service is "unparalleled," says Newman at TIME. Unlike similar services — MOG, Rhapsody, Rdio, and Zune — the perks that Spotify offers at such a low cost makes it likely that potential customers will go for the premium service. Yet the service still doesn't have licenses for songs from the Warner Music Group catalog, says Alex Pham at the Los Angeles Times, meaning a "treasure trove" of music from the likes of Bruno Mars, Green Day, and Eric Clapton won't be available yet. Yet the three other major record labels are a go, which is still a "revolutionary" step for a free music service. Says Geeksugar.com: We're "waiting with headphones ready."

Sources: Billboard, GuardianGeeksugar.com, GizmodoLA TimesTIME, Wired