Quantum billiards are much studied as perhaps the simplest case which presents the central difficulty that the quasiclassical approximation is expressed as a divergent series. We find here, using the Fredholm method, an exact Green's function for billiards expressed as a ratio of absolutely convergent series. We make the quasiclassical approximation to this ratio. The method provides a convergence argument for previous results and an extension of results obtained for the spectrum to the full Green's function.It has been more than twenty years [1] since physicists realized that there is much we have failed to understand in the simplest quantum problems which are not exactly solvable. Among the questions studied are correlations between energy levels and the degree of pseudorandomness of the levels. Similar questions can be asked of wave functions, matrix elements, and scattering amplitudes. Attempts are made to classify the quantum problems, in particular, by the nature of the classical limit, e.g. , whether the classical limit is chaotic [2].Of these problems, doubtless the most thoroughly studied is that of the wave mechanics of a real time independent nonseparable two-dimensional potential. Two further specializations are also commonly made: First (in spite of much evidence that the wave functions are very interesting [3]), the study is restricted to the spectrum, and second, attention is confined to billiards, that is, systems for which the motion is free in the interior, and for which the essential problem is posed by the imposition of conditions on the boundary. Some celebrated billiards are the Sinai billiard, the Bunimovich stadium billiard, and billiards on spaces of negative curvature. Billiards gain