Despite having many unique anatomic features relative to the other digits, the thumb has received little attention in the radiology literature. The thumb, with its opposable and prehensile abilities, enables fine manual dexterity. However, most radiologists have little familiarity with the structures that allow these dynamic movements, other than their recognition of the role of the ulnar collateral ligament in the setting of gamekeeper injury. High-resolution magnetic resonance (MR) imaging allows optimal assessment of the intricate soft-tissue anatomy of the thumb, which enables thumb flexion, extension, abduction, and adduction. Ultrasonography is a readily available, inexpensive tool that can supplement MR imaging in the evaluation of juxta-articular soft-tissue anatomy. Both imaging modalities are extremely useful for identifying the key ligaments responsible for stabilizing the first carpometacarpal and metacarpophalangeal joints. MR imaging is particularly important in assessment of these ligaments in both normal and trauma settings, which is essential for not only recognizing acute injuries but also becoming familiar with the morphologic variations that are potential pitfalls. To accurately and confidently diagnose abnormalities of these small soft-tissue structures, radiologists must have a clear understanding of the complexities associated with imaging the normal thumb anatomy. ©RSNA, 2016.