Description: The Canadian C-Spine Rule was designed in 2001 to assist clinicians assess the need for imaging in people who present to the emergency department with a cervical spine injury following blunt trauma. Specifically, this clinical decision rule was developed for use in adults who are alert (score of 15 on the Glasgow Coma Scale), stable and in whom a clinically important cervical spine injury is a concern (eg, unstable fracture, dislocation). Instructions and scoring: The Canadian C-Spine Rule is based on three high-risk criteria (age ≥ 65 years, dangerous injury mechanism, paresthesia in extremities), five low-risk criteria (simple rear-end motor vehicle collision, sitting position in the emergency department, ambulatory at any time, delayed onset of neck pain; absence of midline cervical-spine tenderness), and the ability of the person to rotate their neck. Reliability, validity and sensitivity to change: The Canadian C-Spine Rule has good-to-excellent inter-rater reliability when applied by physicians (kappa = 0.63), nurses (kappa = 0.80) and paramedics (kappa = 0.93). The sensitivity of the Canadian C-Spine Rule has been reported to range from 90 to 100%, whereas specificity has ranged from 1 to 77%. The large range in specificity reflects the heterogeneity between studies in the number of people who unnecessarily receive imaging (ie, people who do not have a serious cervical spine injury but are still referred for imaging). However, the rule itself errs on the side of caution, as clinicians will not miss a clinically important cervical spine injury. In the only direct comparison, the Canadian C-Spine Rule was found to have better diagnostic accuracy than the National Emergency X-Radiography Utilization Study (NEXUS) criteria, which form another widely used clinical decision rule.