A good number of misconceptions are currently circulating on the effects of non-ionizing radiations on our health, which can lead to an oversimplification of the issue, to potentially dangerous assumptions or to misleading data analysis. Health effects may be exaggerated, or on the contrary underplayed. The authors of this work (doctors, engineers and researchers) have endeavored to supply validated and easily understandable scientific information on the electromagnetic fields and their biological and health effects. After a general review of the physics of the waves and a presentation of non-ionizing radiations, the authors review the main emission sources encountered in our daily environment. They summarize simply but as accurately as possible the current knowledge on their biological effects. The safety limits recommended by international organizations are presented for the different frequency ranges. This book is intended for doctors, teachers, scientists, students, policy makers and anyone else interested in a deeper understanding of the health effects of electromagnetic fields. Intended to serve a broad readership, everyone will approach it according to their respective level of curiosity and knowledge. It is neither an exhaustive inventory of all the studies made to date, nor a survey text focusing only on some chosen studies. Nor is the objective to present all the sources of non-ionizing radiations. Interested readers will be given the opportunity to broaden their knowledge, also by consulting the selected bibliography presented by the authors at the end of each chapter.