The Los Angeles County Metropolitan Transportation Authority (LACMTA), branded as Metro, is the county agency that plans, operates, and coordinates funding for most of the public transportation system in Los Angeles County, California, the most populated county in the United States.

Los Angeles has a complex multimodal transportation infrastructure, which serves as a regional, national and international hub for passenger and freight traffic. The system includes the United States' largest port complex; an extensive freight and passenger rail infrastructure, including light rail lines and rapid transit lines; numerous airports and bus lines; vehicle for hire companies; and an extensive freeway and road system. People in Los Angeles rely on cars as the dominant mode of transportation, but since 1990 the Los Angeles County Metropolitan Transportation Authority has built over one hundred miles (160 km) of light and heavy rail serving more and more parts of Los Angeles and the greater area of Los Angeles County; Los Angeles was the last major city in the United States to get a permanent rail system installed.