  We present the results of a set of high-resolution simulations of the merging
process of two white dwarfs. In order to do so, we use an up-to-date Smoothed
Particle Hydrodynamics code which incorporates very detailed input physics and
an improved treatment of the artificial viscosity. Our simulations have been
done using a large number of particles (4x10^5) and cover the full range of
masses and chemical compositions of the coalescing white dwarfs. We also
compare the time evolution of the system during the first phases of the
coalescence with that obtained using a simplified treatment of mass transfer,
we discuss in detail the characteristics of the final configuration, we assess
the possible observational signatures of the merger, like the associated
gravitational waveforms and the fallback X-ray flares, and we study the
long-term evolution of the coalescence.
