There are at least 6 common types of bearing, each of which operates on different principles:
Plain bearing, consisting of a shaft rotating in a hole. There are several specific styles: bushing, journal bearing, sleeve bearing, rifle bearing, composite bearing.
Rolling-element bearing, in which rolling elements placed between the turning and stationary races prevent sliding friction. There are two main types
Ball bearing, in which the rolling elements are spherical balls
Roller bearing, in which the rolling elements are cylindrical rollers
Jewel bearing, a plain bearing in which one of the bearing surfaces is made of an ultrahard glassy jewel material such as sapphire to reduce friction and wear
Fluid bearing, a noncontact bearing in which the load is supported by a gas or liquid,
Magnetic bearing, in which the load is supported by a magnetic field
Flexure bearing, in which the motion is supported by a load element which bends.