There were about 100 contributors to Rees's Cyclopædia, most of whom were Nonconformists. They were specialists in their fields, covering science, technology, medicine, manufacturing, agriculture, banking and transportation, as well as the arts and humanities. A number were members of the teaching staffs of the Royal Military Academy, and the Addiscombe Military Seminary of the East India Company. Other contributors were working journalists who wrote for scientific, medical and technical periodicals of the time. Several of the contributors were active in radical politics; one was gaoled for sedition and another indicted for treason.