The Ronkonkoma Branch is a rail service operated by the Long Island Rail Road (LIRR) in the U.S. state of New York. On LIRR maps and printed schedules, the "Ronkonkoma Branch" includes trains running along the railroad's Main Line from Hicksville to Ronkonkoma, and between Ronkonkoma and the Main Line's eastern terminus at Greenport. The section of the Main Line east of Ronkonkoma is not electrified and is referred to as the Greenport Branch.

The Main Line is a rail line owned and operated by the Long Island Rail Road in the U.S. state of New York. It begins as a two-track line at Long Island City station in Long Island City, Queens, and runs along the middle of Long Island about 95 miles (153 km) to Greenport station in Greenport, Suffolk County. At Harold Interlocking approximately one mile east of Long Island City, the tracks from the East River Tunnels and 63rd Street Tunnel into Manhattan intersect with the Main Line, which most trains use rather than using the Long Island City station.