Line M may refer to:
M (New York City Subway service), a rapid transit service in New York City Mattapan Line, a light rail line in Boston Marunouchi Line, a rapid transit line in Tokyo M Ocean View, a light rail line in San Francisco Midōsuji Line, a rapid transit line in Osaka Minatomirai Line, a rapid transit line in Yokohama Meijō Line, a rapid transit line in Nagoya Moshtohor, a rabbit breed
See also M line (disambiguation)