This article reviews the nature and use of the journal impact factor and other common bibliometric measures for assessing research in the sciences and social sciences based on data compiled by Thomson Reuters. Journal impact factors are frequently misused to assess the influence of individual papers and authors, but such uses were never intended. Thomson Reuters also employs other measures of journal influence, which are contrasted with the impact factor. Finally, the author comments on the proper use of citation data in general, often as a supplement to peer review. This review may help government policymakers, university administrators, and individual researchers become better acquainted with the potential benefits and limitations of bibliometrics in the evaluation of research.