  Observations of high redshift supernovae indicate that the universe is
accelerating. The hypothesis of `Dark energy' (cosmological constant, scalar
field tracker potentials, braneworld models, etc.) has been advanced to explain
this phenomenon. Sensitive tests of dark energy which can differentiate between
rival models are clearly the need of the hour. The statefinder pair $\lbrace
r,s\rbrace$ is a geometrical diagnostic which can play this role. $r$ & $s$
depend upon the third time derivative of the scale factor $\stackrel{...}{a}$
and provide the next logical step in the hierarchy of the cosmological
parameter set after $H$ and $q$. The statefinder pair $\lbrace r,s\rbrace$ can
be determined to high accuracy from a SNAP type experiment and allows us to
successfully differentiate between dark energy models having constant as well
as time-varying equations of state.
