C1–C2 instability refers to abnormal motion or misalignment between the atlas and axis, the two highest cervical vertebrae responsible for significant neck rotation. This condition may arise from trauma, ligament laxity, inflammatory disease, or congenital anomalies. Patients often experience neck pain, headaches, dizziness, and neurological symptoms due to spinal cord or nerve root irritation. Diagnosis relies on imaging, while management ranges from conservative care and osteopathic treatment to surgical stabilization. Early recognition helps prevent progression and improves long-term outcomes.