Amazon.com Inc. Chief Executive Jeff Bezos is buying the Washington Post for $250 million in an out-of-the-blue deal that captures the newspaper industry's economic decline and the shift of power from old media to Silicon Valley.

The sale puts one of the most famous newspapers in the U.S.—the publication credited with breaking the Watergate scandal that led to President Nixon's resignation almost 40 years ago—in the hands of a Web businessman who rose to prominence only in the past 20 years.

It comes as many newspapers are struggling to survive. Print newspaper ad revenues fell 55% between 2007 and 2012, according to the Newspaper Association of America, as advertisers and readers have defected to the Web. Some newspapers have been forced to slash costs and in some cases file for bankruptcy. Just three days ago the New York Times Co. sold the Boston Globe for $70 million, having paid $1.1 billion for it in 1993.

The Internet is "transforming almost every element of the news business," Mr. Bezos said in a letter to Washington Post employees. "There is no map, and charting a path ahead will not be easy. We will need to invent, which means we will need to experiment," Mr. Bezos wrote.

He added that he won't be involved in the day-to-day management of the newspaper.