Headache is one of the most common types of pain and, in the absence of biological markers, headache diagnosis depends only on information obtained from clinical interviews and physical and neurological examinations. Headache diaries make it possible to record prospectively the characteristics of every attack and the use of headache calendars is indicated for evaluating the time pattern of headache, identifying aggravating factors, and evaluating the efficacy of preventive treatment. This may reduce the recall bias and increase accuracy in the description. The use of diagnostic headache diaries does have some limitations because the patient's general acceptance is still limited and some subjects are not able to fill in a diary. In this chapter, we consider diaries and calendars specially designed for migraine and, in particular, aim to: (1) determine what instruments are available in clinical practice for diagnosis and follow-up of treatments; and (2) describe the tools that have been developed for research and their main applications in the headache field. In addition, we include information on diaries available online and proposals for future areas of research.