Phil Johnson-Laird's theory of mental models has proved to be an influential development in the cognitive sciences. This theory aims to provide a detailed account of both reasoning and inference on the one hand, and language on the other. It can therefore be regarded as a step toward the much-sought-after unified theory of cognition. This book provides an overview of mental models research. Some of the contributors were collaborators or former graduate students of Johnson-Laird, and between them they cover the main strands of mental models theory. After an appreciation of Johnson-Laird, the book covers topics including language processing, reasoning, inference, the role of emotions, and the impact of mental illnesses on thought processes.