The Greater Portland METRO is a regional public transportation system, established in 1966, in Southern Maine.

Several municipalities serviced by METRO withdrew during an age of contraction; service to Yarmouth and Cape Elizabeth ended in 1978, South Portland withdrew in 1983 (although METRO continues to run select buses to the city), and the Portland School Department began operating its own buses in 1985.

The system began to turnaround in the late 1990s, and in 2004 it expanded to Falmouth, which later joined the Greater Portland Transit District.

Portland charter school Baxter Academy for Technology and Science also offers METRO passes to students.

[8][9] In 2024, Greater Portland Transit District began using Equans's NAVINEO computer aided dispatch and automatic vehicle location (CAD/AVL), an intelligent transportation system (ITS), and Optibus, which will assist the company in managing detours in real time, adding or removing trips and will support detailed ridership analysis.

Additionally, the Portland Transportation Center, which provides an intercity bus connection and Amtrak service, serves as a major transfer point.

There is one lettered route, the Husky Line (H), which connects the Gorham and Portland campuses of the University of Southern Maine.

[16] METRO, along with the Biddeford-Saco-Old Orchard Beach Transit, participates in a regional automated fare collection system known as DiriGo Pass.

Instead, passengers load money onto their account and pay fares using a smartcard or the UMO mobile app.

Reduced fares are applicable for persons with disabilities, anyone over 65, veterans, youth ages 6–18, and Medicare card holders.