This introduction chapter provides an overview of the content of the book and outlines a research agenda on freelancing. The Handbook of Research on Freelancing and Self-Employment is intended to provide a single source reference book of research on freelancing in order to facilitate further research as well as inform public policy and business practitioners. The need for the book has been driven by the transformation of freelancing over the last two decades from a predominantly precariat shadow workforce serving as substitutes for employees to a far more diverse workforce incorporating high earning and highly skilled workers who serve a dynamic role for businesses; mainly working as complements to employees and frequently undertaking innovation. This transformation has been paralleled with a rapid rise in the number of freelancers in the workforce and the increasing use of flexible working and outsourcing business models by firms. This book contains research which seeks to explain the causes and implications of these phenomena. It provides a comprehensive overview of research on freelancing both in terms of different types of freelancers and the varying activities they carry out.