Although graphene is extremely inert in chemistry because of the giant delocalized π electron system, various methods have been developed to achieve its efficient chemical modification. Covalent chemistry is effective to modulate the physical properties of graphene. By converting the sp(2) hybridized carbon atoms to sp(3) ones, new two-dimensional (2D) materials and 2D superlattices with fascinating features beyond mother graphene could be built from the graphene scaffold, greatly expanding the graphene family and its attraction. In this Perspective, the power of covalent chemistry is demonstrated from the viewpoint of tailoring graphene's energy band structure as well as creating new 2D materials and 2D superlattices. A specific focus is laid on the general consideration and understanding of covalent graphene chemistry toward electronic devices and material science.