There are three basic types of car seats for infants and older babies: rear-facing, convertible and forward-facing.

• Rear-facing Your baby must ride in a rear-facing seat until he turns 1 and weighs at least 20 pounds--whichever comes last. (The American Academy of Pediatrics recommends that babies remain in the rear-facing position until they reach the maximum height and weight limits allowed by the seat's manufacturer.) But if he reaches the carrier's weight limit before he's 1, or if his head comes to within 1 inch of the top rim of the car seat, he must be moved to a rear-facing convertible seat. Never place a rear-facing car seat in a front seat with an airbag.
Many parents prefer the convenience of an infant carrier--exclusive to rear-facing seats--because the seat can be removed from the car without having to unstrap the baby. (The car-seat base remains in the vehicle; the carrier simply snaps in and out of the base.)

• Convertible This type of seat allows an infant to ride in the rear-facing position from birth until he turns 1 and weighs at least 20 pounds, at which point the seat can be turned around to the forward-facing position. Most convertible seats now accommodate babies in the rear-facing position (the safest way to travel) until they reach 30 or 35 pounds.

• Forward-facing These seats are designed for children who are 1 year or older and weigh 20 pounds or more. Some forward-facing seats convert to belt-positioning boosters when a child reaches approximately 40 pounds.