The California State Guard (CSG) (formerly the California State Military Reserve) is a military unit which provides assistance and training to the California National Guard and is a military force of California. The CSG is a reserve force that supports the state missions and federal readiness of the Army and Air National Guard. CSG service members often come from all branches of the military and are citizens with essential skills. Many CSG service members are fully integrated with Army National Guard and Air National Guard units, and hold full-time state active duty status through the California Military Department.

The California State Guard is authorized under the provisions of the Title 32, United States Code, Section 109(c) and the California State Military Reserve Act (codified in the California Military and Veterans Code). It has legal standing as part of California's Active Militia. Activations are mandatory at times and service members are covered under the Uniformed Services Employment and Reemployment Rights Act (USERRA) as enacted by California state law (7 MVC 394 et. seq. and 566). Employers are required to comply with these laws when service members are called to Emergency State Active Duty (ESAD). Each service member is subject to the Uniform Code of Military Justice (UCMJ) per CMVC § 560.

All citizens over the age of 18 and possessing a high school diploma or GED may apply for enlistment. Military veterans and those with special skills which materially contribute to the National Guard are of particular interest.

CSG service members are normally considered uncompensated state employees, although when called to Emergency State Active Duty (ESAD), they become compensated at the same rate as their National Guard counterparts. Many CSG service members are full-time State Active Duty (SAD).

Training is administered by the Joint Training Command (JTC). The JTC conducts training year round and trains an average of 475 service members per training year.^{[citation needed]}

The JTC provides training, including mission rehearsals, of individuals, units, and staffs using joint service doctrine and tactics, techniques, and procedures (TTPs) to prepare joint forces or joint staffs to respond to strategic, operational, or tactical requirements that are considered necessary to execute their assigned or anticipated missions. All JTC School Houses utilize the Train, Assess, and Counsel method when conducting training.^{[citation needed]}

Any MOS, awards, medals, or badges earned in federal service transfer to the CSG. Depending on rank and time since separation, previous rank also transfers. CSG service members are held to the same regulations and training requirements for promotion as their National Guard counterparts.^{[citation needed]}

All new members must attend the Basic Training Course (BOC). New members without prior military experience must attend Initial Entry Training (IET), a three-month Asynchronous Learning online course where members report to a student learns the fundamentals of the CSG. They are given monthly homework and E-Learning tasks to strengthen their knowledge and train how to interact with the chain of command. Each month new materials are released and students are exposed to another element of becoming a proficient member of their Unit and the CSG. Members are required to maintain physical fitness standards, done on their own time.^{[citation needed]}