The scope of clinical research is to evaluate the effect of a treatment on the evolution of a disease in the human species. The treatment can be pharmacological, surgical, psychological/behavioral or organizational/logistic. The disease, intended as an impairment of a state of well-being or a condition capable of provoking such impairment over time, can be universally accepted as such (e.g. a cancer or a bone fracture) or perceived as such only by limited groups of individuals in a given cultural context (e.g. hair loss or weight gain). The course of the disease that ones wishes to change can be the one with no intervention or, more frequently, the one observed with the available treatment. The evaluation of the effect of a treatment on the course of a disease is a lengthy process, which progresses in increasingly complex stages. A detailed coverage of the logistic, administrative and legal aspects of clinical research is outside the scope of this book. However, throughout the book we keep reminding the reader of these aspects because, as already mentioned, we firmly believe they have a crucial role in determining the success of a study. The history of clinical research is paved with relics of studies started with great pomp, riding great ideas and great hopes, which drowned miserably because of inadequate logistical preparation. In our experience, the excessive complexity of a clinical trial is the single most frequent cause of failure: the study is perfect on paper, but impossible to implement by patients and staff alike. The distance between the principal investigators and the reality of clinical research in its day-to-day practice is often the main cause of such disasters. We warmly encourage everyone involved in clinical research to get involved in the logistics of a study, learning from colleagues responsible for its practical conduct (clinical research associates, data managers, etc.) and to take part, in person, in the practical implementation of a trialbefore attempting to design a study protocol. The book ends with a brief description of the drug development process and to the phases of clinical development.