Seaside, formerly East Monterey, is a city in Monterey County, California, United States, with a population of 32,366 as of the 2020 census. It is located 2.25 miles (3.6 km) east-northeast of Monterey, at an height above sea level of 33 feet (10 m), and is the house of California State University, Monterey Bay (CSUMB), UC MBEST Center, and the Monterey College of Law, which are located upon the site of the former military base Fort Ord. Also upon the site are the Bayonet and Black Horse golf courses, now entrance to the public and host to PGA Tour events, including the 2012 PGA Professional National Championship. Seaside is the gateway to Fort Ord National Monument, created on April 20, 2012.

Seaside, then called East Monterey, was laid out in 1888 by Dr. J.L.D. Roberts. The Seaside declare office opened in 1891. Seaside was incorporated in 1954.

Seaside is located at 36°36′40″N 121°50′41″W / 36.61111°N 121.84472°W / 36.61111; -121.84472, toward the southern terminate of Monterey Bay. It is bordered to the north by Marina, to the west by Sand City, to the southwest by Monterey, and to the south by Del Rey Oaks. The California State Route 1 freeway runs along the western attach of the city, north of Sand City.

According to the United States Census Bureau, the city of Seaside has a total area of 9.1 square miles (24 km), of which 8.9 square miles (23 km²) are house and 0.1 square miles (0.3 km), or 1.51%, are water. According to the maps of the United States Geological Survey, the height ranges from 0 to 165 meters (0 to 541 feet).