NEW YORK—Google May 26 introduced Google Wallet, the search engine's long-rumored mobile payment service. The free service, unveiled at an event at Google's sprawling New York office, includes a free Google application that users can download to tap their phone and pay for goods from participating merchants, such as RadioShack. Citigroup and MasterCard are providing the mobile purchase services, which will be enabled by special point of sale registers equipped with near-field communications (NFC). NFC is the wireless technology that enables devices equipped with special chips and sensors to communicate when brought in close proximity to one another. Though little used in the U.S., Google officials said they expect NFC to roll out on 50 million smartphones in the next few years. Sprint is partnering with Google to offer its Samsung Nexus S 4G smartphone for this experimental service. The Nexus S 4G, which includes an NFC controller chip from NXP, runs Google's Android 2.3 "Gingerbread" operating system, which includes native NFC support. Google Wallet is coming to New York and San Francisco in a trial run this summer, with expansion to additional cities and smartphones in the future. Coca-Cola vending machines and even taxis are PayPass-enabled, including major outlets such as CVS, Jack in the Box, Sports Authority and Sunoco. Take this picture tour of the service in this eWEEK slide show, which we composed live from the event.