What is science? Is it a set of demonstrated truths or just a method to advance knowledge? How do we know that the scientific method is valid? Why should scientific results be published and discussed in specialized journals? What practical rules must scientific research follow? Science is not a pipe dream; it is a social human activity. It is not an infallible and definitive knowledge, but a task for searching and questioning. It is the most reliable way to generate the knowledge that humanity has developed. This book is part of the study of science as an activity and presents practical guidelines to design projects, conduct research, publish results and participate in the collective task of building more and better knowledge. In a single volume, it summarizes the various branches of the theory of science and the main practical aspects of its methodology. This book is a must for researchers and students from all disciplines.