Human bipedal walking can be both stable and energetically efficient in complex envi ronments. Previous research in the field has primarily addressed how the lower limbs are controlled to ensure this stability and efficiency. However, little is known about how the trunk contributes towards gait stability and energetic efficiency. To address this gap, I proposed four novel studies that investigated the role of trunk in human gait. In the first study, I demonstrated that the trunk plays a more important role in stability during very slow walking compared to walking at the typical speeds of healthy humans. The second study investigated how the trunk is utilized to maintain stability in winter weather conditions in Canada, finding that there was no alteration to the use of the trunk in the winter. To investigate if the trunk compensated for restrictions to other stability strategies, the third study involved walking with restric tions while perturbations were applied. These experiments revealed that there was no additional contribution of the control of the trunk to maintaining stability when other strategies are restricted. The final study investigated how trunk angle affects the mechanics and energetic cost of gait during sloped walking. I found that the pre ferred trunk flexion coincides with minimum metabolic cost, and increased hip work with greater trunk flexion also leads to decreased work at the knee and angle. The results overall lead to the conclusion that the trunk is narrowly used to maintain sta bility but still offers work trade-offs that can reduce energy expenditures. These four studies served to improve the scientific understanding of how the trunk is controlled in order to maintain stability and energetic efficiency during walking.