Let G be any Carnot group. We prove that, if a subset of G is contained in a rectifiable curve, then it satisfies Peter Jones' geometric lemma with some natural modifications. We thus prove one direction of the Traveling Salesman Theorem in G. Our proof depends on new Alexandrov-type curvature inequalities for the Hebisch-Sikora metrics. We also apply the geometric lemma to prove that, in every Carnot group, there exist −1-homogeneous Calderón-Zygmund kernels such that, if a set E ⊂ G is contained in a 1-regular curve, then the corresponding singular integral operators are bounded in L 2 (E). In contrast to the Euclidean setting, these kernels are nonnegative and symmetric.