A high back booster seat does not come with a seat belt. It is designed to be used with the rear seat belt that is installed with your vehicle. However, many high back booster seats are convertible. This means that they come complete with a harness system for use with younger children that are below the height and weight requirements for a booster seat. Once converted into a high back booster however, the harness is no longer needed, and the vehicle’s seatbelt should be used.