The craniocervical junction (CCJ) is a complex region of the spine that protects and provides a functional conduit for the spinal cord, several nerve roots, and major blood vessels. Damage and injury to the CCJ results in neurologic deficit or in severe cases even morbidity. There is not much known about the biomechanics of the pediatric CCJ. Lack of pediatric cadaver poses a substantial barrier to experimental biomechanical studies. The adult CCJ, on the other hand, is relatively better understood. However, there is still a knowledge gap in our understanding of the role that ligaments play in stabilizing a normal pediatric and adult CCJ. In this dissertation, finite element (FE) models of the pediatric and adult CCJ were developed to assess their biomechanics and the role that CCJ ligaments play in providing stability. The pediatric FE model developed for this dissertation is the only subject-specific pediatric CCJ model currently published in the literature. The results of this pediatric CCJ FE model showed that when adult material properties were scaled to 10%, the model predictions closely matched averaged experimental range of motion data for a similar age cohort of cadaveric specimens. Sensitivity studies carried out with the adult models showed that the occipitoatlantal capsular ligaments are the primary stabilizers of the occipitoatlantal joint and that the atlantoaxial capsular ligaments and the transverse ligament are the primary stabilizers of the atlantoaxial joint. The models in this dissertation were developed with an open-source software suite called FEBio (Finite Elements for Biomechanics) and will be made freely available to the research community. This dissertation has established a computational framework for investigating pediatric and adult CCJ biomechanics. Furthermore, it provides valuable insights into the biomechanics of the pediatric and adult CCJ. The data presented adds to our current understanding of the role that ligaments play in CCJ stability and challenges the current paradigm of CCJ instability diagnoses by shifting the focus away from clinico-radiographic indicators of instability to evaluating biomechanical considerations while diagnosing instability.