Abstract: Haugen, TA, Tønnessen, E, Svendsen, IS, and Seiler, S. Sprint time differences between single- and dual-beam timing systems. J Strength Cond Res 28(8): 2376–2379, 2014—Valid and reliable measures of sprint times are necessary to detect genuine changes in sprinting performance. It is currently difficult for practitioners to assess which timing system meets this demand within the constraints of a proper cost-benefit analysis. The purpose of this investigation was to quantify sprint time differences between single-beam (SB) and dual-beam (DB) timing systems. Single-beam and DB photocells were placed at 0, 20, and 40 m to compare 0–20 and 20–40 m sprint times. To control for the influence of swinging limbs between devices, 2 recreationally active participants cycled as fast as possible through the track 25 times with a 160-cm tube (18 cm diameter) vertically mounted in front of the bike. This protocol produced a coefficient of variation (CV) of 0.4 and 0.7% for 0–20 and 20–40 m sprint times, respectively while SEM was 0.01 seconds for both distances. To address the primary research question, 25 track and field athletes (age, 19 ± 1 years; height, 174 ± 8 cm; body mass, 67 ± 10 kg) performed two 40 m sprints. This protocol produced a CV of 1.2 and 1.4% for 0–20 and 20–40 m, respectively while SEM was 0.02 seconds for both distances. The magnitude of time differences was in the range of ±0.05–0.06 seconds. We conclude that DB timing is required for scientists and practitioners wishing to derive accurate and reliable short sprint results.