As early researchers in molecular communication, we have been amazed by the rapid expansion of the field. A decade ago, virtually nobody worked in this area; today, dozens of researchers form a multi-national research community, and over a hundred papers have been published. At the frontiers of the field, there are fundamental questions to be answered such as the relationship between information theory and biology; and disruptive innovations to be developed, such as direct manipulation of structures in the human body at a microscopic level.

Given the advances over the past few years, we believe the time is right to take stock of the field and publish a complete overview of the state of the art. In an interdisciplinary field such as this one, we hope this book can provide a needed common point of reference. Moreover, in an evolving field such as this one, we recognize that our book should not be considered the final word on the field. Indeed, in writing it we have become fully aware of the many important open problems and research questions that need to be addressed for this field to reach its potential, and we hope our book is viewed as an invitation to further research, to expand upon this exciting new discipline.