The Clark papers are an indispensable source for the study of the history of the Observer newspaper, the early days of political broadcasting, postwar politics in Britain and the United States and Third World issues. The papers consist of:
- Diaries and notebooks
- General correspondence and papers
- Special correspondence and papers
- Broadcasts, speeches and lectures
- Correspondence and papers relating to publications
- Printed memorabilia and press cuttings
- Photographs and miscellanea
- Additional papers (received 1990), mainly concerned with his Presidency of the International Institute for Environment and Development, 1980-5