Embodied conversational agents (ECAs) are autonomous software entities with human-like appearance and communication skills. These agents can take on a number of different roles, for example, as an assistant, tutor, information provider, or customer service agent. They may also simply represent or entertain a user. The precise nature and benefits of different characteristics of ECAs requires careful investigation. Questions range from the function of an eyebrow raise to mechanisms for assessing and improving ECA trustworthiness. This book will help experts and designers in the specification and development of applications incorporating ECAs. Part 1 provides guidelines for evaluation methodologies and the identification of design and evaluation parameters. Part 2 demonstrates the importance of considering the user's perspective and interaction experience. Part 3 addresses issues in fine-tuning design parameters of ECAs and verifying the perceived effect. Finally, in Part 4 lessons learned from a number of application case studies are presented. The book is intended for both ECA researchers in academia and industry, and developers and designers interested in applying the technology.