Paradata, also termed ‘process data’, contain information about the primary data collection process (e.g. survey duration, interim status of a case, navigational errors in a survey questionnaire, etc.). Paradata can provide a means of additional control over or understanding of the quality of the primary data (the responses to the survey questions). This entry describes how paradata can be collected, some of their uses, and some data preparation issues that may need to be addressed before paradata can be analyzed. While describing uses of paradata, most attention will be paid to paradata collected in web surveys on the process of completing the web questionnaire.