This is heavy, Doc!

Way back in 1985, Marty McFly and Doc Brown (aka Michael J. Fox and Christopher Lloyd) went Back to the Future, jumping forward in time to Oct. 21, 2015. For those of us who saw Back to the Future Part II in theaters back in 1989, that date is synonymous with "the future," and we've been waiting decades for it to arrive. At last, it's nearly here.

To celebrate both "Back to the Future — Future Day" (totally just made that up) and the 30th anniversary of the original film, Universal Pictures has partnered with Amazon.com to offer the entire Back to the Future trilogy to Amazon Prime subscribers for free.

Throughout the entire month of October 2015, you can fire up your Amazon Prime Video app or visit it in your browser, and stream these three modern classics to your heart's content. Amazon Prime subscribers can begin streaming Back to the Future immediately.

Don't forget: The 30th Anniversary Special Edition release of the trilogy on Blu-ray is coming on Oct. 20, 2015. It's loaded with special features you won't find streamable on Amazon Prime, including a new short film starring Christopher Lloyd as Doc Brown.

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