  We consider the geometry of spacetime based on a non-metric, Finslerian,
length measure, which, in terms of physics, represents a generalized clock. Our
defnition of Finsler spacetimes ensure a well defined notion of causality, a
precise description of observers and a geometric background for field theories.
Moreover we present our Finsler geometric extension of the Einstein equations,
which determine the geometry of Finsler spacetimes dynamically.
