As the county seat, Martinez, also known as Martínez in Spanish, is a city in Contra Costa County, California, located in the East Bay neighborhood of the San Francisco Bay Area on the southern coast of the Carquinez Strait. The city was named after Ygnacio Martínez, a Californio ranchero, and it was established on his Rancho El Pinole. Martinez is renowned for its charming historic center and picturesque waterfront.

Long, hot, dry summers with generally clear skies, as well as brief, cold, and wet winters with partly cloudy skies, are the norm in Martinez. 40°F to 83°F is the typical temperature range for the entire year. There are only very infrequent instances where it goes below 32°F or above 93°F. Beginning on June 4 and lasting until October 10, the warm season has an average daily high temperature of over 78°F and lasts for about 4.2 months. On the other hand, the cool season lasts 2.5 months, from November 28 to February 12, with a daily maximum average temperature that is lower than 60°F.

The major employers in Martinez, according to the City's 2021 Comprehensive Annual Financial Report, are Contra Costa County (10,065 employees), Veterans Health Administration (962 employees), and Kaiser Permanente (730 employees). Other major employers include Equilon Enterprises, Martinez Unified School District, Wal-Mart, Safeway, City of Martinez, The Home Depot, and Brand Energy & Infrastructure Service, each contributing significantly to the city's workforce.

Education in Martinez is provided by the Martinez Unified School District, which comprises four elementary schools, one middle school, one high school, and two alternative/independent study schools. The district's comprehensive high school is Alhambra High School, while grades 6 through 8 are served by Martinez Junior High School and students attend elementary schools including John Swett, John Muir, Las Juntas, or Morello Park Elementary School. Additionally, St. Catherine of Siena School, a private Roman Catholic elementary school, serves the Martinez community. A portion of Martinez is also serviced by the Mount Diablo Unified School District. Meanwhile, the National Register of Historic Places has recognized the Contra Costa County Library, a municipal library system, for its Art Deco architecture.

In Martinez, transportation options include WestCAT, which provides service to the El Cerrito del Norte BART station, and the County Connection, the primary local bus operator with destinations to Concord, Pleasant Hill, and Walnut Creek BART stations. Tri Delta Transit also offers express service between Martinez and eastern Contra Costa County. State Route 4 runs through the city, connecting westward to Hercules and eastward to Stockton and the Sierra Nevada. Interstate 680 passes through Martinez via the Benicia-Martinez Bridge, connecting to Sacramento and San Jose. Additionally, Amtrak provides passenger rail services through Martinez, including the California Zephyr, Coast Starlight, Capitol Corridor, and San Joaquin trains, offering connections to various destinations in California, Nevada, and Oregon. The city also has plans for a potential BART line extension in the future. The Muir Trestle, also known as the Alhambra Trestle, carries freight operations of the BNSF Railway through Martinez alongside California State Route 4.