  A new analytical approach to the motion and radiation of (comparable mass)
binary systems has been introduced in 1999 under the name of Effective One Body
(EOB) formalism. We review the basic elements of this formalism, and discuss
some of its recent developments. Several recent comparisons between EOB
predictions and Numerical Relativity (NR) simulations have shown the aptitude
of the EOB formalism to provide accurate descriptions of the dynamics and
radiation of various binary systems (comprising black holes or neutron stars)
in regimes that are inaccessible to other analytical approaches (such as the
last orbits and the merger of comparable mass black holes). In synergy with NR
simulations, post-Newtonian (PN) theory and Gravitational Self-Force (GSF)
computations, the EOB formalism is likely to provide an efficient way of
computing the very many accurate template waveforms that are needed for
Gravitational Wave (GW) data analysis purposes.
