  We give an introduction to Joyce's construction of the motivic Hall algebra
of coherent sheaves on a variety M. When M is a Calabi-Yau threefold we define
a semi-classical integration map from a Poisson subalgebra of this Hall algebra
to the ring of functions on a symplectic torus. This material will be used in
arxiv:1002.4374 to prove some basic properties of Donaldson-Thomas
curve-counting invariants on Calabi-Yau threefolds.
