A convertible car seat is a rearward seat (facing the back car window) suitable for newborns to  30 months old (approximately). It also converts to an upright forward seat (facing the driver) from 12 months to 4 years (guide only). The seat has an in-built harness and stays secured in your vehicle. You can adjust the seat position as your child grows (shoulder markers indicate when they're ready for the next height).