Retaining brackets to fixedly secure either a singular modular shelving unit or multiple modular shelving units are disclosed. The retaining brackets can prevent modular shelves from dislodging, by positioning the retaining bracket such that an opening on the retaining bracket aligns with a mounting location on a vertical member of the modular shelving unit, and a distance between a retaining surface of the retaining bracket and a top surface of the modular shelf is small enough to prevent dislodging of the modular shelf when the retaining bracket is installed. The retaining surface of the retaining brackets can vary depending on the configuration used to retain the modular shelf, as well as the embodiment of the retaining bracket used.