  We present a first-principle computation of the mass distribution of jets
which have undergone the grooming procedure known as Soft Drop. This
calculation includes the resummation of the large logarithms of the jet mass
over its transverse momentum, up to next-to-logarithmic accuracy, matched to
exact fixed-order results at next-to-leading order. We also include
non-perturbative corrections obtained from Monte-Carlo simulations and discuss
analytic expressions for hadronisation and Underlying Event effects.
