To protect Americans from serious infectious diseases and other health threats, public health authorities conduct national case surveillance to monitor more than 120 diseases and conditions. For these conditions, public health collects information on individuals with the infection in a population, which is known as case surveillance. The goal of case surveillance is to provide information necessary to control outbreaks and inform public health action. Case surveillance is especially important for new diseases, such as COVID-19, in order to understand the similarities and differences between cases, including: demographic, clinical, and epidemiologic characteristics, exposure and contact history, and course of clinical illness and care received. During the COVID-19 response, state and jurisdictional health departments voluntarily report to CDC using the National Notifiable Diseases Surveillance System. Data about COVID-19 cases are sent to CDC without personal identifiers, such as names or home addresses. A national standardized case definition is used to define confirmed and probable cases and deaths. Unlike data collected for clinical trials and research studies in which scientists comprehensively measure and follow the health status of a patient, national case surveillance data focuses on capturing demographic and risk factor information about people with COVID-19.