The Eclipse infrastructure for modeling is based on EMF, an implementation of Essential MOF, the OMG standard for metamodeling. A recent addition to EMF has been parametric polymorphism (also known as “parameterized types” or “generics”) thus achieving the same benefits realized in other generic type systems (most notably, Java 5). To our knowledge, this is the first formal account in the literature of the resulting type system, including the well-formedness rules (WFRs) for type expressions. We offer an initial formalization of the type system of EMF Generics by formulating those WFRs in OCL (Object Constraint Language). The insights thus gained are applicable to solve the type-checking problem for custom DSLs (Domain Specific Languages).