This paper presents a review of approaches to text visualization and exploration. Text visualization and exploration, we argue, constitute a subfield of data visualization, and are fuelled by the advances being made in text analysis research and by the growing amount of accessible data in text format. We propose an original classification for a total of 49 cases based on the visual features of the approaches adopted, identified using an inductive process of analysis. We group the cases (published between 1994 and 2013) in two categories: single-text visualizations and text-collection visualizations, both of which can be explored and compared online.