Through computerized text analysis, the psychology of literature is on the threshold of becoming a dominant force in psychology and the social sciences. The ways people use words in their writing and in everyday life reflect people's social and psychological states. Whereas most text analysis research has focused on the content of people's writings, the current paper demonstrates that almost-invisible function words can be psychologically relevant as well. Through the analysis of pronouns, prepositions, and other function words used in literature, several studies demonstrate how authors' emotional states, aging processes, theories of mind, and the nature of their romantic and collaborative relationships are revealed through their words. The function word approach provides a glimpse of the rapidly expanding methods available to psychologists interested in tracking the social and psychological worlds of authors. With the upcoming release of data sets such as Google Books, the analysis of literature will likely serve as a foundational method used in the fields of psychology, linguistics, history, and other areas of the behavioral and social sciences.