We propose new concepts of statistical depth, multivariate quantiles, vector quantiles and ranks, ranks, and signs, based on canonical transportation maps between a distribution of interest on IR d and a reference distribution on the d-dimensional unit ball. The new depth concept, called Monge-Kantorovich depth, specializes to halfspace depth for d = 1 and in the case of spherical distributions, but, for more general distributions, differs from the latter in the ability for its contours to account for non convex features of the distribution of interest. We propose empirical counterparts to the population versions of those Monge-Kantorovich depth contours, quantiles, ranks, signs, and vector quantiles and ranks, and show their consistency by establishing a uniform convergence property for empirical (forward and reverse) transport maps, which is the main theoretical result of this paper.1. Introduction. The concept of statistical depth was introduced in order to overcome the lack of a canonical ordering in IR d for d > 1, hence the absence of the related notions of quantile and distribution functions, ranks, and signs. The earliest and most popular depth concept is halfspace depth, the definition of which goes back to Tukey [54] Zuo and Serfling [62], who list four properties that are generally considered desirable for any statistical depth function, namely affine invariance, maximality at the center, linear monotonicity relative to the deepest points, and vanishing at infinity (see Section 2.2 for details). Halfspace depth is the prototype of a depth concept satisfying the Liu-Zuo-Serfling axioms for the family P