The craniovertebral junction (CVJ) is a highly mobile segment of the axial skeleton consisting of the occiput (O), atlas (C1), and axis (C2), with extensive ligamentous support to maintain the necessary balance of motion and restriction. While rare, CVJ neoplasms such as chordomas, meningiomas, and metastases can lead to significant instability in this critical region through either osseous destruction or cytoreductive surgery. Occipitocervical fusion (OCF) is the standard definitive intervention for tumor-associated occipitocervical instability. While surgical technique and instrumentation options have evolved significantly over time, postoperative misalignment still remains a significant challenge. This chapter will review the relevant surgical anatomy involved in OCF, describe the evolution of modern instrumentation and special considerations for instrumentation choice and timing for patients with CVJ tumors, and emphasize key craniocervical alignment parameters to optimize functional outcomes and limit complications.