Cardiff-by-the-Sea, usually referred to as Cardiff, is a beach community in the incorporated city of Encinitas in San Diego County, California. The Pacific Ocean is to the west of Cardiff-by-the-Sea, the rest of incorporated Encinitas is to the east and north, and a beach and lagoon to the south. With a population of under 12,000, Cardiff-by-the-Sea operates as part of the city of Encinitas, but unlike the other communities that comprise Encinitas, has its own ZIP code (92007). Cardiff is home to a few well-known surf spots, such as Swami's and Cardiff Reef.

Encinitas is a beach city in the North County area of San Diego County, California. Located within Southern California, it is approximately 25 miles (40 km) north of San Diego, between Solana Beach and Carlsbad, and about 95 miles (153 km) south of Los Angeles. As of the 2020 United States census, the city had a population of 62,007, up from 59,518 at the 2010 census.