The primary function of the Constable's Department is Civil Process and the execution of warrants. As provided in the Texas Constitution, The Texas Code of Criminal Procedure, and the Texas Rules of Civil Procedure, Constable's and their deputys may execute and return any process, civil or criminal. This includes any warrant, citation, notice, subpoena, summons, or writ in Bexar County, or in certain cases, contiguous counties. Constables are the chief process servers of the Justice Courts. Constables are often called upon to serve process for County and District Courts. They are responsible for the safekeeping of property seized under various writs and exercise a wide range of criminal law enforcement authority including traffic enforcement, community crime prevention, and narcotics investigations. The Constable's office is also responsible for the security of the Justice Court.

The Constable's Department Precinct Three serves civil and criminal process originating in the Justice of the Peace Courts, District Courts, and County Courts-At-Law. Through state statute, Constables are mandated to attend to the Justice of the Peace Courts in their respective precinct, including providing baliff services, transporting prisoners, and summoning jurors. Due to the County wide focus of decreasing and detering juvenile crime, Constables are becoming more involved with truancy issues and are assisting many school districts by helping to educate parents and students alike.