Online text visualization tools are a recent phenomenon on the World Wide Web. The potential of these tools to improve reading comprehension has not yet been empirically researched. Therefore, this book investigates if online text visualization tools can help to improve reading comprehension. In the empirical research a quasi-experimental method was applied. The data were collected via tests distributed among the students of an experimental group and a control group. The results of the tests show that both groups improved during the practice on the same topic. However, the students of the experimental group who had training with the tools improved more than the students of the control group. According to the results, the use of text visualization tools helped the students of the experimental group to improve their reading comprehension.