  We study the spin-1/2 Heisenberg antiferromagnet on a bilayer honeycomb
lattice including interlayer frustration. Using a set of complementary
approaches, namely Schwinger bosons, dimer series expansion, bond operators,
and exact diagonalization, we map out the quantum phase diagram. Analyzing
ground state energies and elementary excitation spectra, we find four distinct
phases, corresponding to three collinear magnetic long range ordered states,
and one quantum disordered interlayer dimer phase. We detail, that the latter
phase is adiabatically connected to an "exact" singlet product ground state of
the the bilayer which exists along a line of maximum interlayer frustration.
The order within the remaining three phases will be clarified.
