Existing formalisms of inheritance are not sufficient to model the complexities of the kind of multiple inheritance exemplified in C++.Any satisfactory formalism must model the complicating effects of virtual and nonvirtual base classes as well as virtual and non-virtual methods.By abstracting the implementational notion of a subobject and formalizing subobject selection, we develop a formalism to model this combination of features.Not intended as a formal semantics of C++, the resulting model should nevertheless provide an essential level of understanding for language theorists and implementors in their dealings with C++ and related languages.