Abstract. We establish the existence of an asymptotic expansion as t -► 0+ for the trace of the heat kernel for the Neumann Laplacian in a bounded Lipschitz domain. The proof of an asymptotic expansion for the heat kernel for the Dirichlet Laplacian is also sketched. The treatment of the Dirichlet Laplacian extends work of Brossard and Carmona who obtained the same result in C1 -domains.A classical question in analysis asks: What is the relationship between the spectrum of the Laplacian on a domain and the geometry of the domain? This question has been studied by many authors including [1,3,7, 11,12,14,15,17,19]. One approach to this problem proceeds by considering the trace of the heat semigroup on D,where g is the heat kernel on D and 0 < Ai < A2 < A3•• • is the sequence of eigenvalues for -A on D.One attempts to give an asymptotic expansion for tx(g) near t = 0 whose coefficients are quantities associated with the geometry of D. Thus one can deduce geometrical information about D from knowledge of the spectrum.In this paper, we will address this question under minimal smoothness assumptions on the boundary of D. In particular, we will obtain asymptotic expansions for tx(g) when the order of smoothness of the boundary corresponds exactly to the order of accuracy of the asymptotic expansion.In order to state our main theorem, we need one definition: By a Lipschitz domain, we mean a bounded connected open set whose boundary may be locally described as the graph of a Lipschitz function. Our main result is Main Theorem. Suppose that D c R" is a Lipschitz domain, then the heat kernel for the Laplacian with Dirichlet boundary conditions on 3D satisfies tx(g)(t) = (4ntyn'2 (\D\ -^^n~x(dD) + o(txl2)\ .