Maryland Route 118 is the "main street" and major thoroughfare for the Washington, D.C. suburb of Germantown, Maryland. It is also known over its entire 7-mile (11 km) length as Germantown Road, and is commonly referred to by locals as "one-eighteen". It is located entirely in Montgomery County, Maryland.

The road starts as a four-lane road at Maryland Route 28 near Darnestown, quickly condensing to two lanes at it begins its northward path. It passes through residential areas on Germantown Road and then enters a forest, where it bridges Great Seneca Creek. It continues north, passing by a large electrical substation and passes through more forest before it enters a residential development in southern Germantown. Here, the road widens to four lanes, with a median, as it passes through the town. It crosses the MARC Train's Brunswick Line and then interchanges at Exit 15 of Interstate 270. After this interchange, Maryland Route 118 lanes range between four and six as it continues east to its end at Maryland Route 355 near the Neelsville neighborhood in Germantown. Germantown Road, however, continues east of this intersection.

Points of interest along MD 118 include several shopping centers, Germantown Town Center (including, just off 118, the Germantown Library and the Black Rock Center for the Arts), the United States Department of Energy Germantown complex, South Germantown Recreational Park, and the Maryland SoccerPlex. The farm property to which Washington Senators' Hall of Fame baseball pitcher Walter Johnson retired is near the intersection of Route 118 and Wisteria Road; less than 500 feet (150 m) southeast of that intersection is a small section of road named in his honor.

A major new intersection with the extended Father Hurley Boulevard will be completed in late 2011. This will connect the existing four to six-lane section of Father Hurley Boulevard (which turns into MD 27 at MD 355) that lies north of the CSX right of way with the residential two-lane section of Father Hurley Boulevard that lies in a residential neighborhood south of the CSX tracks. The entire portion of Father Hurley south of the rail tracks will be widened and rebuilt as a designated a "four lane Major Dual Highway" and connect to Route 118 between MD 117 and Dawson Farm Road. This is expected to reduce congestion on Route 118 through the Town Center of Germantown by providing an alternate bypass route from I-270 to points south and west of the Town Center.

The entire route is in Montgomery County.