The purpose of this booklet is to help the reader to become aware of the volume of Earth resources data that have been collected by agencies of the United States Government and to find out where and how these data may be obtained. Earth resources data as discussed here are those obtained by remote-sensing instruments, including aerial cameras, multispectral cameras, multispectral scanners, and radar. They are obtained by spacecraft and high-altitude aircraft. Also, various agencies have been acquiring vast quantities of conventional aerial mapping photography from low and medium altitudes for more than 50 years. There is also brief information to assist the reader in locating published references and identifying research projects relating to application of Earth resources data to a variety of purposes. In all cases, it is not the intent to say what data are needed or how the data are to be used, but to describe where an interested person can begin to locate Earth resources data.