  We discuss the inverse problem of determining the possible presence of an
(n-1)-dimensional crack \Sigma in an n-dimensional body \Omega with n > 2 when
the so-called Dirichlet-to-Neumann map is given on the boundary of \Omega. In
combination with quantitative unique continuation techniques, an optimal
single-logarithm stability estimate is proven by using the singular solutions
method. Our arguments also apply when the Neumann-to-Dirichlet map or the local
versions of the D-N and the N-D map are available.
