There is disclosed a process and apparatus for induction hardening of the flank, root and tip surfaces of the teeth of a gear so as to provide surface-hardened layer along said surfaces. An electrically energizable inductor head carries out traversing movement along the space between a pair of adjacent gear teeth, the inductor head having an external profile substantially matching the profile of the space between the gear teeth and having the height of the inductor head less than the depth of the space between the root and tip surfaces of each pair of gear teeth. Guides maintain predetermined clearances between the inductor head and the tooth surfaces which define the tooth space, during traversing movement of the inductor head [the clearance being a minimum between the inductor head and the root surface and varying in predetermined manner along the flank surfaces] in such a way as to achieve heating along the flanks and root surfaces to a substantially uniform predetermined temperature suitable for induction hardening. The entire gear is immersed in a tank of coolant and jets of coolant are directed to the surfaces of the unheated flanks, the tips, the heated flanks and the root of the pair of gear teeth so as to achieve relatively rapid cooling of said surfaces. As a result, a substantially uniform thickness surface-hardened layer from tip to tip along the flanks and root surfaces of the pair of gear teeth is achieved so that each tooth is able to withstand more reliably the tensile stresses which are applied to gear teeth, when intermeshing gear teeth apply fatigue bending loads to each other.