  We present two method for optimal entanglement concentration from pure
entangled states by local actions only. However a prior knowledge of the
Schmidt coefficients is required. The first method is optimally efficient only
when a finite ensemble of pure entangled states are available whereas the
second method realizes the single pair optimal concentration probability. We
also propose an entanglement assisted method which is again optimally efficient
even for a single pair. We also discuss concentrating entanglement from
N-partite cat like states.
