The autopilot system is capable of keeping aircraft stabilized in all three axes laterally, longitudinally, and vertically. Early autopilot systems did this function during cruise only, but most autopilot now controls all flight from take-off to landing.
The main purpose of the autopilot system is to relieve the flight-crew of controlling the aircraft’s attitude for the entire duration of the flight.
There are many autopilot systems available in the industry but they feature a wide range of capabilities and complexity. High-performance transport categories of aircraft have autopilots with higher capabilities than light aircraft.