The MAX Orange Line is a light rail line in TriMet's MAX light rail system. The MAX system has been operating in the Portland, Oregon region since the 1980s, and the Orange Line was the fifth line to be added, opening in September of 2015. The line serves the south part of Portland, and Portland's immediate southward suburb of Milwaukie, running six miles from downtown Portland to Milwaukie, and stopping at 12 stations along the way.

Although the idea of a light rail line serving the southern areas of Portland had been around a long time, the actual construction of the line did not begin until 2009. The largest obstacle to the construction of the light rail line was the fact that the tracks were on the west side of the Willamette River, and the line would serve the east side of the river. This was solved through the construction of the Tilikum Crossing, a large, cable-stayed bridge that carries exclusively light rail, The Portland Streetcar, TriMet buses, as well as pedestrians and bicyclists. Building this bridge was the single largest engineering challenge of the Orange Line, but it was constructed on schedule and under budget. The Orange Line has been successful since its opening, and now averages over 10,000 daily riders.

The Orange Line represents the last part of the second line of lightrail construction for TriMet, which begin in 2001 with the opening of the Airport Red Line, and included the Yellow Line in 2004 and the Green Line in 2011. This exhausts the list of high density suburbs that don't present topographical challenges, and the next scheduled line, to Tigard, involves the technically challenging project of crossing the West Hills. There is a possibility that the Orange Line could be continued south to Oregon City, but this is not currently being actively planned.

One problem with the Orange Line is that while its tracks are actually a continuation of the Yellow Line serving North Portland, it is not an efficient way to get from North Portland to South Portland and Milwaukie. The reason for this is that it passes through downtown, which has frequent stops, and where the trains must travel slowly enough to deal with traffic there. Thus, the train takes almost as much time going through two miles of downtown Portland as it does on the actual part of its route. This design flaw comes from the divided nature of the MAX system: although it is a light rail system, in some parts of its route it functions more as a commuter rail system, while in the center of Portland it functions more as a tram or trolley. At the time the system was designed, it wasn't planned to have extended as much as it has, and the slow times through downtown were merely an inconvenience. Like so much in Portland, the Orange Line is effected by how much has been transformed in the past thirty years, and that the MAX system was initially designed for a Portland that no longer exists.