:For the demolished freeway in Portland, Oregon, see Harbor Drive.

The Harbor Freeway is one of the principal north-south freeways in Los Angeles County, California. Signed as Interstate 110 (abbreviated I-110) for its entire length, it runs from Gaffey Street in San Pedro to the Santa Monica Freeway (Interstate 10) south of downtown Los Angeles, where it turns into the Pasadena Freeway and becomes signed as California State Highway 110. The Harbor Transitway is a grade-separated bus and high-occupancy vehicle in the median between State Route 91 (Gardena Freeway) and the south side of downtown Los Angeles.

Even though the Harbor Freeway legally ends at Interstate 10 (see below), "Harbor Freeway" does appear on freeway signs north of the Santa Monica Freeway up to U.S. Route 101 and the Four Level Interchange in downtown Los Angeles.

The Harbor Freeway, along with the Long Beach Freeway, are the principal means for freight to get from the port of Los Angeles to rail yards and warehouses further inland. Its interchange with the Santa Monica Freeway is notoriously busy and congested, and the portions bordering Bunker Hill in northwest downtown Los Angeles are choked with traffic at peak travel times.

The I-110 number was once used for the stub of the San Bernardino Freeway (mostly I-10) west of the I-5. The Harbor Freeway was originally signed as California State Highway 11 until 1981 and was for a time signed as U.S. Highway 6.

The Harbor Freeway is noted for its elaborate high-occupancy vehicle lane infrastructure, with HOV lanes elevated above the rest of traffic in many areas. Of particular note is the 7-story ramp that connects the eastbound Century Freeway to its northbound carpool lanes, offering splendid views of the entire Los Angeles Basin and the San Gabriel Mountains, weather permitting.