Eugene Garfield and his Institution for Scientific Information (ISI) helped revolutionize information retrieval in the second half of the twentieth century by introducing the concept of citation indexing for scientific literature. Science Citation Index data also served as a foundation for quantitative studies in the history and sociology of science and eventually gave birth to the field of scientometrics. From its founding in 1960 until its sale to Thomson Corporation in 1992, ISI introduced a range of current awareness and information retrieval products and services covering the literature of the sciences, social sciences, and humanities. Other products, such as the Journal Citation Reports, permitted analysis of citations as measures of communication and research performance. ISI colleague Henry Small, with the support of Garfield, introduced science mapping in the 1970s to reveal the socio-cognitive structure of research. Clarivate Analytics acquired the ISI product range from Thomson Reuters Corporation in 2016 and today continues the original business and intellectual legacy of Garfield.