This book addresses important findings, assumptions, problems, hopes, and future guidelines on the use of advanced research techniques to study the moment-by-moment mental processes that occur while a reader or listener is understanding language. The core techniques are eye tracking and ERPs, with some extensions to others such as fMRI. The On-line Study of Sentence Comprehension has been written by top researchers in the field of psycholinguistics, who are also leading experts in the use of eye tracking and ERPs. This book combines comprehensive overviews of the state of the art on theoretical progress, the latest on assumptions behind the use of eye movements (reading and visual world) and ERPs methods with papers that address specific research questions. This work covers not only methodological issues but also discusses the theoretical progress in understanding language processing using temporally fine-grained methods.