Printed circulars of the Extension Service in Agriculture and Home Economics, which were published irregularly for distribution to farmers, advisers, and the public, as well as for government use in special programs. Early circulars were published in two series, Extension Circulars and Experiment Station Circulars. These were combined in 1921 with Experiment Station Circular 247. Since 1940, starting with Circular 510, the series has been designated as Extension Service Circulars.
The circulars include booklets, full-length volumes, guides, and pamphlets. Subjects vary widely, ranging from highly technical agricultural information (concerning crop yields, pest control, fertilizer, and other best practices) to guides for raising children, investing, building homes, and daily life. Also included is a 1940 index to circular topics, which contains lists of related publications and materials.