A hybrid boost bearing assembly is described for a rotating shaft member which is rotatably supported on a base member. The hybrid boost bearing assembly comprises a rolling element bearing for rotatably supporting the shaft member on the base member during starts, stops, reverse thrust loadings and under emergency operating conditions, and a fluid film bearing acting singly or coacting with the rolling element bearing for absorbing the loads imposed on the shaft member during all other conditions of operation. A fluid lubricant supply is provided for supplying fluid lubricant to the bearings and means are provided for shifting the loading of the rotating shaft member from the rolling element bearing to the fluid film bearing as the rotating shaft member is brought up to its normal operating speed. The means for shifting the loading from the rolling element bearing to the fluid film bearing comprises the generation of pressure in the fluid film space between the opposed fluid film bearing surfaces, by hydrodynamic action, from an external source of pressure, or by some other means, thereby causing the fluid film bearing to assume a greater share of the load of the rotating shaft as it is brought up to normal operating speed. As a result, the rolling element bearing will assume substantially the full load of the rotating shaft only during starting, stopping, reverse loading periods, and in the event of the failure of the fluid lubricant supply, while the fluid film bearing will absorb the shaft loads under all other conditions of operation. The fluid film bearing may comprise a hydrodynamic bearing for producing a self-acting fluid film, a hydrostatic bearing, or a hybrid hydrodynamic-hydrostatic bearing, and the rolling element bearing may comprise a ball bearing, roller bearing, needle bearing, or the like. In certain arrangements a preloading spring is provided for preloading the rolling element bearing a predetermined amount so that the rolling element bearing assumes a predetermined proportionate share of the loading on the rotating shaft under certain operating conditions. In other arrangements, a retractable bearing piston portion which moves towards and retracts from an opposed, load-sustaining bearing surface is employed to cause the fluid film bearing to assume the load from the rolling element bearing. In other arrangements, a spherically-shaped self-aligning seat is provided which coacts with a complementary-shaped seating surface to accommodate misalignment in the rotating shaft supported by the bearing assembly.