Abstract: In this paper we propose a combinatorial model for sketch recognition. Two fundamental problems, the evaluation of individual symbols and the interpretation of a complete sketch scene possibly containing several symbols, are expressed as combinatorial optimization problems. We settle the computational complexity of the combinatorial problems and present a branch and bound algorithm for computing optimal symbol confidences. To handle sketch scenes in practice we propose a modest restriction of drawing freedom and present an algorithm which only needs to compute a polynomial number of symbol confidences.