Diaries are a research tool that require respondents to regularly record their daily activities and experiences. They can be open-format or highly structured, depending on the level of detail required. Diary studies typically last long enough to capture behaviors or events of interest. Different types of diaries include paper-based, email-based, text-based, voice-based, and social media-based. Diaries are useful for collecting sensitive information and as a supplement to interviews, as respondents can record entries in their own time and a wide range of people can participate without training. However, diaries also have limitations such as incomplete entries, lack of cooperation from some, and difficulty verifying accuracy.