As there are no validated biomarkers for primary headache disorders, e.g., migraine, diagnosis for these diseases rely on the medical history with possible assistance of a range of screening tools. Diagnostic criteria for headache disorders are provided by The International Classification of Headache Disorders, third edition (ICHD-3). The ICHD-criteria were developed to harmonize diagnosis of headache disorders across regions; this was of particular interest for researchers as it allowed for consistent and comparative data. For the same reason, the ICHD-3 prioritizes specificity over sensitivity. However, there are situations where time restraints, e.g., primary care, or specific setups, e.g., epidemiological research, warrant employment of screening tools or patient-reported questionnaires that allow for rapid diagnosis with a relatively high sensitivity and specificity. In this chapter, we focus on clinical instruments for diagnosing and screening of headache and migraine. In addition, we highlight red flags, green flags, and screening tools for headache.