Physics. An Introduction is a book for anyone who wants to know the fundamentals of this science and its application in the natural world. Through a multitude of examples in which physics plays a central role, it explains in a rigorous but simple way how bodies move, what energy is, what we know about light and electromagnetic radiation, or the dynamics of fluids, without forgetting quantum physics and relativity. The book contains all the physics necessary to form an opinion on current issues, such as renewable energies or climate, and conveys a precise idea of what this experimental science consists of.The book is suitable for self-taught learning beyond college, but also for formal training in one semester physics subjects in degrees such as environmental sciences, biology, architecture or geology, since it covers all the contents at the required level, in a narrative form, with a minimal mathematical apparatus, and providing examples that help motivate students. It is in fact the contents taught by the author in the last two decades in the in the environmental sciences degree program at UCLM.