Breast and bra motion research aims to understand how the breasts/bra move to aid development of apparel that minimizes motion. Most previously published research has tracked nipple motion to represent bra motion. However, this method does not provide information regarding regional tissue motion. A more comprehensive approach might facilitate understanding how the entire soft-tissue mass moves during physical activities. This study developed and tested an objective method to comprehensively measure 3-dimensional bra motion, including regional displacement and velocity, displacement phasing, and surface stretch. To test the method, 6 females were fitted with a minimally supportive, seamless bra (small bra n = 3; large bra n = 3). Data were collected as participants ran on a treadmill. Results indicated marker displacement, velocity, link stretch, and link stretch velocities reached as high as 52.6 (6.8) mm, 504.8 (88.7) mm/s, 29.5% (7.1%) of minimum length, and 3.8 (1.0) mm/s/mm, respectively, with the large bra having greater motions compared with the small. Most bra motion occurred above/below the nipple region and at the bra’s strap–body interface, independent of bra size. Importantly, maximum marker displacement and velocity did not occur at the nipple. Measurements obtained from this new method may be important for designing innovative clothing that minimizes bra motion during physical activity.