Henry Small is currently serving part-time as a research scientist at Thomson Reuters. He was formerly the director of research services and chief scientist. He received a joint PhD in chemistry and the history of science from the University of Wisconsin. He began his career as a historian of science at the American Institute of Physics' Center for History and Philosophy of Physics where he served as interim director until joining ISI (now Thomson Reuters) in 1972. He has published over 100 papers and book chapters on topics in citation analysis and the mapping of science. Dr Small is a Fellow of the American Association for the Advancement of Science, an Honorary Fellow of the National Federation of Abstracting and Information Services, and past president of the International Society for Scientometrics and Infometrics. His current research interests include the use of co-citation contexts to understand the nature of inter-disciplinary versus intra-disciplinary science as revealed by science mapping.