An introductory chapter to the book discusses the purpose and target of the book. It discusses the relevance of comparative approach to the start-up law. This chapter offers an insight into the development of this project and its initiation in 2017, when a course ‘How to Start a Start-up’ was introduced at the Faculty of Law, University of Copenhagen. The book is an open source publication for start-ups, entrepreneurs and their lawyers and advisors. This book aims to become an instrument for lawyers and current and future entrepreneurs. This book offers a comparative understanding into the life cycle of start-ups. This book helps navigate the decision-making processes and understand the business and legal elements that founders need to undertake in different periods of the life of the company. This book offers five jurisdictions from three continents, while following the same original structure: the lifecycle of a start-up.