  Variable-Speed-of-Light (VSL) cosmologies are currently attracting much
interest as a possible alternative to cosmological inflation. We discuss the
fundamental geometrodynamic aspects of VSL cosmologies, and provide several
alternative implementations. These implementations provide a large class of VSL
cosmologies that pass the zeroth-order consistency tests of being compatible
with both classical Einstein gravity and low-energy particle physics. While
they solve the ``kinematic'' puzzles as well as inflation does, VSL cosmologies
typically do not solve the flatness problem since in their purest form no
violation of the strong energy condition occurs. Nevertheless, these models are
easy to unify with inflation.
