D Line may refer to:
Transportation United States D (Los Angeles Railway), a former streetcar line in Los Angeles, California D (New York City Subway service), a subway route in New York D (SEPTA Metro), a trolley line in Delaware County, Pennsylvania D Line (Los Angeles Metro), a rapid transit line in Los Angeles County, California D Line (RTD), a light rail line in Denver Green Line D branch, a light rail line in Boston, Massachusetts Metro D Line (Minnesota), a bus rapid transit line in Minneapolis, Minnesota RapidRide D Line, a bus route in Seattle, Washington
Europe Line D (Prague Metro), a subway route under construction in Prague, the Czech Republic Line D (Rome Metro), potential line of the Rome Metro system D Line (Paris), one of the RER five lines serving Paris and its suburbs Argentina Line D (Buenos Aires Underground), an underground line in Buenos Aires, Argentina
Other uses Defensive line, commonly referred to as D-line, a formation in gridiron football D-line, Port Harcourt, a neighborhood in Port Harcourt, Nigeria D-line (IRC), a command in IRCd D-line, a spectral line of the Fraunhofer lines
See also D Train (disambiguation) Eth, a Latin-script letter represented by Ð