A method of grouping sheet units, which belong together in sheet groups, a sheet stream comprising two superposed sheet units each by means of a grouping unit, a grouping unit for a sheet handling system, and a sheet handling system that allow a high processing speed and a high cycle efficiency of a sheet handling system are disclosed. A sheet unit can be held back in the grouping unit. Depending on whether the downstream subsequent sheet units transferred into the grouping unit belong to a sheet group, the held-back sheet unit can be released by itself and together with one or together with both downstream subsequent sheet units.