  We review the fictitious integrable system approach which predicts dynamical
tunneling rates from regular states to the chaotic region in systems with a
mixed phase space. It is based on the introduction of a fictitious integrable
system that resembles the regular dynamics within the regular island. We focus
on the direct regular-to-chaotic tunneling process which dominates, if
nonlinear resonances within the regular island are not relevant. For quantum
maps, billiard systems, and optical microcavities we find excellent agreement
with numerical rates for all regular states.
