Google will purchase your unwanted patents in order to keep them out of the hands of "patent trolls."
With company dynamics constantly changing, often times companies find themselves in possession of patents that they no longer need. Selling a patent, especially for smaller companies, can be a difficult task, and Google looks to make that easier with an experimental Patent Purchase Promotion. In an effort to keep these patents out of the hands of "patent trolls", Google is asking people to submit their patents, along with an asking price, and Google will decide if they wish to purchase or not.
Unfortunately, the usual patent marketplace can sometimes be challenging, especially for smaller participants who sometimes end up working with patent trolls. Then bad things happen, like lawsuits, lots of wasted effort, and generally bad karma. Rarely does this provide any meaningful benefit to the original patent owner.
The experimental promotion runs from May 8, 2015 through May 22, 2015, and then Google will evaluate the submissions. After reviewing the submissions Google will make contact by June 26, 2015 to those whom they wish to purchase from, and move forward with the sale.
Source: Google Public Policy