It is over 50 years since Dr. Eugene Garfield envisioned citation indexing tools that would allow researchers to expedite their research process, evaluate the impact of their work, spot scientific trends, and trace the history of modern scientific thoughts. Dr. Garfield went on to build a company – ISI (now part of Clarivate) around these ideas. Here we bring together essays and articles written by Dr. Garfield and other Clarivate staff members, to provide in-depth explanatory information for users of our citation databases and other information tools.