Flatfoot deformity is a common disorder of the foot and ankle and is caused by loss of the hindfoot arch. Radiologists and clinicians should be familiar with the anatomy and the imaging criteria used to assess injury to the supporting structures. Radiographs and computed tomography are most useful in characterizing the degree of osseous deformity and ultrasonography and MR imaging are most useful in the evaluation of the supporting soft tissue structures. Treatment depends on the clinical symptoms and involves restoring the normal biomechanics of the hindfoot arch through strengthening exercises, foot/ankle orthotics, and surgery.