Recent years have seen the development of several foundational models for statically typed object-oriented programming. But despite their intuitive similarity, differences in the technical machinery used to formulate the various proposals have made them difficult to compare. Using the typed lambda-calculus F^ω_<: as a common basis, we now offer a detailed comparison of four models: (1) a recursive-record encoding similar to the ones used by Cardelli, Reddy, Cook, and others; (2) Hofmann, Pierce, and Turner's existential encoding; (3) Bruce's model based on existential and recursive types; and (4) Abadi, Cardelli, and Viswanathan's type-theoretic encoding of a calculus of primitive objects.