NSK Slewing Bearings or slew[ing] ring is a rotational rolling-element bearing that typically supports a heavy but slow-turning or slow-oscillating load, often a horizontal platform such as a conventional crane, a swing yarder, or the wind-facing platform of a horizontal-axis windmill.

Compared to other rolling-element bearings, slewing bearings are thin in section and are often made in diameters of a metre or more; the slewing bearings on the Wheel are 4 metres diameter and fit over a 3.5 metre axle.

Slewing bearings often use two rows of rolling elements. They often use three race elements, such as an inner ring and two outer ring "halves" that clamp together axially.