  We analyze the space-times admitting two shear-free geodesic null
congruences. The integrability conditions are presented in a plain tensorial
way as equations on the volume element $U$ of the time-like 2--plane that these
directions define. From these we easily deduce significant consequences. We
obtain explicit expressions for the Ricci and Weyl tensors in terms of $U$ and
its first and second order covariant derivatives. We study the different
compatible Petrov-Bel types and give the necessary and sufficient conditions
that characterize every type in terms of $U$. The type D case is analyzed in
detail and we show that every type D space-time admitting a 2+2 conformal
Killing tensor also admits a conformal Killing-Yano tensor.
