It's been a busy summer for Square. After having already struck deals with Walgreens, Staples, and FedEx, the mobile payment specialist has now announced a major partnership with Starbucks. Under the deal, customers at participating US Starbucks outlets will be able to pay for products using the Pay with Square app, in addition to the dedicated Starbucks app already available on both iOS and Android.

Square will also integrate its directory function within the Starbucks app, allowing customers to locate other Square partners within their vicinity. Starbucks will begin accepting Square payments this fall, at approximately 7,000 locations across the US.

Starbucks has also pledged to invest $25 million as part of Square's latest round of financing, with CEO Howard Schultz joining Square's board of directors. In a statement, Schultz praised his company's new partner, lauding Square's platform as "an essential tool to jump-start" any small business.

The deal certainly gives a major boost to Square, which has seen a surge of competition in recent months. Starbucks now becomes its largest retail partner, and should help the company expand its reach even further. Earlier this summer, Square announced that it now processes more than $6 billion a year in mobile payments, marking a major jump from its projection of $4 billion, announced just three months earlier.