Google Fi Wireless (pronounced /faɪ/), formerly Project Fi and Google Fi, is an American MVNO telecommunications service by Google that provides telephone calls, SMS, and mobile broadband using cellular networks and Wi-Fi. Google Fi uses the T-Mobile network. Google Fi is a service for US residents only, as of late 2023.

The service was launched for the Nexus 6, by invitation only, on April 22, 2015. The service was opened to the public on March 7, 2016. It began to work with additional device models, including the Pixel and Pixel XL smartphones, on October 4, 2016. On November 28, 2018, Google rebranded Project Fi as Google Fi and made it work with more device models, including partially with iPhones. In 2023, it was once again renamed Google Fi Wireless.

Google Fi was announced exclusively for the Nexus 6 smartphone on April 22, 2015, on the Sprint and T-Mobile networks. Because of high demand at launch, the service required that users receive invitations, which were gradually released throughout summer 2015. The invitation system was dropped on March 7, 2016. U.S. Cellular was added on June 8, 2016. Three was added on July 12, 2016. In October 2016, Google added the ability to use Pixel and Pixel XL smartphones, and later introduced a Group Plan, letting subscribers add extra members to their plans.

In February 2023, Google Fi and US Cellular discontinued their partnership, leaving T-Mobile as the only network usable with it in the US.

Prior to the merger of Sprint and T-Mobile, Google Fi Wireless automatically switched between its partner networks depending on signal strength and speed. It automatically connects to open Wi-Fi hotspots while securing data with encryption through an automatic VPN. Phone calls transition to a cellular network if Wi-Fi coverage is lost.

Google Fi Wireless users could originally use the now defunct Google Hangouts on any phone, tablet, or computer to call and text. There is still a web interface for voice, texts, and voicemail available if you turn off RCS Chats in Google Messages.

Google Fi Wireless also implements VoLTE as part of a staged rollout.

In addition to using a phone's physical SIM card, Google Fi offers a Bring Your Own Device (BYOD) option whereby the customer uses their compatible phone (Google Pixel, Android or iPhone) using an eSIM (embedded SIM) virtual card to establish Google Fi as a standalone service or in conjunction with another provider. When a phone uses the DualSim, the phone owner can make and receive telephone calls from either Google Fi or the other mobile provider, but only one of the data service can be used at a time.