The Zoe app is a mobile application that runs on Android and iOS devices. There are two versions of the app: the Zoe Health Study and Zoe Personalized Nutrition. The Zoe Health Study, formerly known as the COVID Symptom Study, is a health research project of British company Zoe Limited that tracks COVID-19 symptoms and other salient data in a large number of people to enable epidemiological results to be calculated. The app was created in 2020 in response to the COVID-19 pandemic, in a collaboration between Zoe, Kings College London, Guys and St Thomas Hospitals, with funding granted by the UK government until April 2022. On the other hand, Zoe Personalized Nutrition is a program that analyzes an individuals unique gut, blood fat, and blood sugar responses to improve their long-term health and reach a healthy weight. The program starts with the most comprehensive at-home test available, analyzing an individuals gut microbiome, blood sugar, and blood fat to get an accurate picture of their unique biology. The app uses machine learning and the microbiome to understand how gut microbes influence an individuals health and weight. Zoe Personalized Nutrition is designed and built by Zoe Global Limited, a health science start-up, in partnership with doctors and scientists at Kings College London.