We describe Links, a low-level calculus designed to serve as the basis
for an intermediate representation in compilers for class-based
object-oriented languages.  The primitives in Links can express a wide
range of class-based object-oriented language features, including
various forms of inheritance, method override, and method dispatch.
In particular, Links can model the object-oriented features of Moby,
Ocaml, and Loom, where subclasses may be derived from unknown base
classes.  Links can also serve as the intermediate representation for
more conventional class mechanisms, such as Java's.  In this paper, we
formally describe Links, give examples of its use, and discuss how
standard compiler transformations can be used to optimize programs in
the Links representation.