Planetary gearsets are indispensable power transfer components in several mechanical systems, and are preferred over their parallel-axis counterparts due to their coaxial arrangement, high power density, minimal radial loads, and multiple possible kinematic combinations. Despite these benefits, the complex arrangement of components in a planetary gear system makes them susceptible to noise and vibration issues. These challenges become multifold with the advent of electric drive units, not only due to their high operating loads and speeds but also due to the fact that there is no broadband noise from the engine to mask the transmission noise. Considering the aforementioned issues with planetary gears and lack of accurate and computationally efficient analysis tools, this dissertation presents a three-dimensional dynamic load distribution model for planetary gearsets. The proposed formulation uses a numerical integration scheme in conjunction with an iterative elastic contact algorithm to solve the multibody contact problem, and unlike previous models can implicitly capture the influence of probable assembly and manufacturing errors in a planetary gearset. As powertrain components are continually being optimized to their design limits, the baseline formulation is further extended to capture the influence of additional system compliances due to; input/output shaft, carrier, planet pin, and ring gear, flexibilities. The effects of various component and system level design parameters on the dynamic response of gearset are studied using the proposed model, to comprehend the system’s behavior better and identify relevant metrics to assess its performance. Further, to validate the proposed model, a unique experimental methodology was developed to synchronously measure multiple quasi-static responses of a simple four-planet gearset, namely planet load sharing, overall transmission error, and floating sun gear orbits. An extensive set of experiments were performed to study the influence of design parameters such as planet mesh phasing, gear tooth modifications, and carrier pin position errors on the system’s behavior. These measurements constitute the most extensive experimental database to date for quasi-static planetary gear testing. Owing to its computational efficiency and validated fidelity, the developed model for planetary gears has immense industrial viability and is generic enough to be extended to other types of gears.