  We study quantum walks on general graphs from the point of view of scattering
theory. For a general finite graph we choose two vertices and attach one half
line to each. We are interested in walks that proceed from one half line,
through the graph, to the other. The particle propagates freely on the half
lines but is scattered at each vertex in the original graph. The probability of
starting on one line and reaching the other after n steps can be expressed in
terms of the transmission amplitude for the graph. An example is presented.
