Two months ago Amazon moved into the market for digital books with the introduction of Kindle, its portable wireless book reader. Now, the mega retailer and book seller has announced it has agreed to acquire Audible.com, a digital distributor of audiobooks, for approximately $300 million in cash and short-term investment.

Although Amazon is an online vendor it still primarily sells hard-copy books, CDs, and DVDs by mail, so the move is another step forward for the company into the digital distribution realm. Looking to cover its bases in terms of content distribution in music, books, and movies, the company also launched its movie download service, Unbox, back in 2006 and has been building a DRM-free digital music store to compete with Apple’s iTunes.