Originating from the diverse perspectives of an anthropologist, a poet, and a filmmaker, the Mass Observation project undertook an extensive documentation of British society, between 1937 and the early 1970s, with particular strength in the period 1937-1955. The online collections is drawn from the archive of the organization held at the University of Sussex.  Adam Matthew began microfilming portions of the archive in twelve parts in 1994.

The digital archive and its initial update includes selected materials from the Sussex archive, including indexed diaries, surveys, studies, full-text reports, maps, and photographs.  More than three thousand previously unpublished pages of materials are included. The bulk of the digital archive, however, consists of finding aids to the rest of the source materials.

The collection contains two main sets of documents. One is the empirical data and personal writings collected by the Mass Observation organization, the Topic Collections and the Day Surveys. Highlights include approximately five hundred indexed diaries and surveys from 1939 to 1942 centered on specific themes, such as dancing, shopping, and television. The second set includes the File Reports and Publications frrom 1937-1972: published and unpublished reports written on the basis of the surveys and reseaerch, as well as 25 out-of-print books written by members of the Mass Observation staff. The digital archive also includes bibliographic summaries of data and documents from topic collections focused on dreams, radio listening, and reading habits spanning the period 1937 to 1950. The publisher reports that the only overlap between the microfilm and the online version consists of the 6,000 pages of published documents, out of 234,000 total scanned pages of material.

Mass Observation Online is useful for cultural research in history, anthropology, sociology, literature, and gender studies, and not just specific to British society. Because the survey and data-gathering methodologies of the Mass Observation researchers are considered amateurish by today's standards, the collection would be especially useful for undergraduates.  It includes contextual essays describing the significance of the materials and two essays written by graduate students recounting their experiences with the archive. A CRL member noted, “Its appeal is not restricted to historians of the United Kingdom. The aim of the Mass Observation Project was to examine how modern citizens engaged in their world, the UK being merely the empirical site of the investigation.”