This book is primarily for newcomers to sciences, technology, engineering, and medicine interested in the field of electromagnetic radiation's non-laser and laser sources and their applications. The book concisely discusses the sources' emission mechanisms, fabrication, generated radiation properties, and limitations. The classification of laser sources is emission mechanism-based, unlike the traditional classification of solids, liquids, and gases. Also, this book clears a few misconceptions about laser description from earlier books. It emphasizes the research and commercial applications of lasers; non-laser techniques are not included. The applications where non-laser methods are included discuss lasers' advantages and disadvantages. The repetition of some basic concepts in the book is intentional to provide sufficient background for a new idea.