The majority of the contributors to this book are members of the London Mental Models Group (see below for a fuller deSCription of this group). Between the years 1989 and 1992 this group was engaged in a major research programme, the Tools for Exploratory Learning Programme, examining the nature of children's reasoning when they are working with modelling tools, and it is this research that forms the basis for this book. Other members of the London Mental Models Group, and other friends outside the group, were simultaneously working on aspects of modelling within education. In this book we have put together contributions from these colleagues working within their own projects around a structure derived from the research design of the Tools for Exploratory Learning Programme. This book therefore reports on some five years of very exciting and diverse research activities, and aims to begin to create some form of synthesis of this work.