This technical report summarizes the GLOBE Observer data set from 1 April 2016 to 1 December 2019. GLOBE Observer is an ongoing NASA-sponsored international citizen science project that is part of the larger Global Learning and Observations to Benefit the Environment (GLOBE) Program, which has been in operation since 1995. GLOBE Observer has the greatest number of participants and geographic coverage of the citizen science projects in the Earth Science Division at NASA. Participants use the GLOBE Observer mobile app (launched in 2016) to collect atmospheric, hydrologic, and terrestrial observations. The app connects participants to satellite observations from Aqua, Terra, CALIPSO, GOES, Himawari, and Meteosat. Thirty-eight thousand participants have contributed 320,000 observations worldwide, including 1,000,000 georeferenced photographs. It would take an individual more than 13 years to replicate this effort. The GLOBE Observer app has substantially increased the spatial extent and sampling density of GLOBE measurements and more than doubled the number of measurements collected through the GLOBE Program. GLOBE Observer data are publicly available (at observer.globe.gov).Plain Language Summary GLOBE Observer is a NASA citizen science mobile application ("app") that gives anyone with a smartphone or tablet the opportunity to share what they see in the sky and on the landscape around them. GLOBE Observer is available for free from Google Play and the Apple App Store. Since 2016, tens of thousands of people around the world have taken hundreds of thousands of observations. An individual scientist would have to work non-stop for more than 13 years to make the same number of observations. All of the data sent through GLOBE Observer go into a worldwide database that's made freely available to everyone (at observer.globe.gov). This article describes how the GLOBE Observer app works and shows what 3 years of data look like.