Bicycles may have eyelets, tapped with a standard thread, at the dropouts on the rear chainstays, and on the front fork blades.
A style of rack clamps only to the seatpost, does not require eyelets or additional hardware, but has a limited capacity.
Luggage carriers can be mounted on recumbents and on folding bicycles, but may require customization or additional hardware.
Additionally, specialized or customized luggage carriers are often required on bicycles with (rear) disc brakes or full suspension.
A common type of child seat designed for carrying an infant on a bicycle mounts to a rear luggage carrier.
Some luggage carriers have an extra, lower, rail to hang panniers on, this provides better stability and more space on the platform.