The service, which was initially announced in May, lets people with mobile phones running on Google’s Android mobile operating system upload credit and debit card information to a “mobile wallet.” Starting Thursday, shoppers will be able to use their phone to pay at more than one million retail stores in the U.S. that have point-of-sale registers equipped with near field communication technology, known as NFC.

Google (GOOG) said Android Pay will support credit and debit cards from the four major payment networks including Visa (V), MasterCard (MC), American Express (AXP), and Discover (DFS). Early partners for Android Pay include Whole Foods, Macy’s, and McDonalds.

Android Pay is Google’s attempt to play catch up with Apple Pay, the rival service from Apple (AAPL). Apple has a head start of a year, although its services are only compatible on phones using Apple’s proprietary operating system, iOS.

In many ways, Android Pay is similar to Apple Pay. That includes security measures.

Android Pay incorporates fingerprint biometrics to authenticate payments, whereby people verify their identity by pressing their finger onto their phone’s screens. Apple Pay allows authentication using its Touch ID technology.

Both say their services are secure because they never share credit card numbers with merchants.

But they differ when it comes to shopping within apps rather than brick and mortar stores. Apple Pay supports so called in-app payments while that won’t be available on Android Pay until later this year. Google is working on lining up as many app developers as it can. In May, it said Lyft, the ride hailing service, would support Android Pay so that its customers could use the service to pay within its app.

Android Pay will also differ from Apple Pay in that it will be available on many existing Android devices at launch including older phones. Currently, seven out of ten Android phones in the U.S. are equipped for Android Pay.

To get Android Pay, users can simply download the app from the Google Play store. In comparison, Apple Pay was dependent on NFC hardware built into the iPhone 6 last year and was unavailable on older models.

Google says that Android Pay will also be preinstalled on new NFC-enabled Android phones from AT&T, T-Mobile and Verizon Wireless.

Android Pay will face competition on certain Android phones from Samsung’s payments technology, Samsung Pay. Similar to Android Pay, Samsung Pay uses NFC technology to let users make payments in a store using their phones and stored credit cards.

For Google, Android Pay represents the latest evolution in its push to power mobile payments. For years, it has tried but failed to win over users with mobile wallets. In 2011, the search giant introduced Google Wallet, which also used NFC technology, for Android phones. But the service never caught on.

Google is betting that technology is easier to use and that consumers are now ready to change their shopping habits. Google also hopes that it can benefit from Apple’s relative success in popularizing mobile payments with the public.

Android Pay’s precursor, Google Wallet, is still available, although it has evolved. In May, Google said that mobile app would transition into a service for digitally transferring money to anyone, replacing cash or checks. The app works by users linking their Wallet accounts to their debit and credit cards. Google said that the new version of Google Wallet would also be rolled out Thursday.

Market research company Juniper Research recently reported that the number of mobile wallets using NFC technology is expected to reach 200 million by the end of 2016, double from the end of 2014, thanks to Apple Pay (Android Pay had not launched when this study was released).

For more about the mobile payments wars, watch this video: