Purpose: To determine the effect of in-season differential training on volleyball spike-jump technique and performance in elite-level female players. Methods: During the season, spike jumps of 12 elite female players (Austrian Volleyball League Women) were recorded by 13 Qualisys Oqus cameras (250 Hz) and an AMTI force plate (1000 Hz). First measurement was made at the beginning of the investigation. Two identical measurements were repeated after a first and a second interval. The first interval served as control phase. The second interval was comparable in length and regular program but included differential training (6 wk, 8 sessions of 15–20 min) as a modified warm-up. It addressed specific performance determinants. Analyses of variances were calculated for the 3 measurements and for the development during control and intervention phase. Results: Initial jump height (0.44 [0.09] m) changed by −4.5% during the control phase and +11.9% during the intervention (P < .001, ${\eta }_{\mathrm{p}}^2=.70$). All approach variables, arm backswing, and velocity-conversion strategy improved compared with the control phase (Δ%: 6.1–51.2%, P < .05, ${\eta }_{\mathrm{p}}^2=.40-.80$). Joint angles, countermovement depth, maximal angular velocities, and torso incline were not affected (Δ%: −2.9–9.1%, P = .066–.969, ${\eta }_{\mathrm{p}}^2=.00-.27$). Conclusions: In-season differential training led to technical adaptations and increased spike-jump height in elite female players. The differential training program allowed players to experience a range of adaptability and to adjust toward an individual optimum in technical components of performance determinants. Coaches are encouraged to apply technical differential training to elite athletes and to target biomechanical performance factors specifically.