Abstract: A sport boot adapted in particular to gliding on snow, ice or hard ground, having an outer sole adapted to be made integral with a gliding member if necessary, and from which an upper extends to cover the skater's foot, wherein the boot has two parts, the first of which, made from a relatively rigid material, constitutes a cradle forming a rear envelope adapted to house the skater's heel and extending forward to constitute the sole, which is adapted to be made integral, during assembly, with a second part, made from a relatively flexible material, constituting a vamp covering the skater's forefoot, having a plantar support, that is nested then respectively connected to the cradle by fixed connecting elements that are implemented after a relative adjustment of the vamp in the longitudinal direction with respect to said cradle, between at least two positions corresponding to at least two successive sizes, the vamp furthermore including deformation zones allowing its nesting in the cradle.