  We report a practical non-postselection entanglement concentration scheme in
which a maximally entangled Bell-state photon pair is produced from two pairs
of partially (or non-maximally) entangled photons. Since this scheme is built
only upon linear optical elements and does not require photon-number resolving
detectors, it has immediate applications in experimental implementations of
various quantum information protocols which require two-photon Bell-states.
