Living beings are made up of organic molecules, proteins, nucleic acids, sugars and fats. All of them are compounds whose main base is carbon. Organic products are present in all aspects of our lives: the clothes we wear, the soaps, shampoos, deodorants, medicines, perfumes, kitchen utensils, food, etc. It is so called because for a time it was believed that these compounds came from living organisms, a theory known as the "vital force". Despite its late appearance in the history of chemistry, the chemistry of carbon compounds is currently the branch of chemical science that grows fastest. The variety of products derived from carbon can be practically unlimited due to the unique properties of that atom and, therefore, constitutes a potential source of new materials with special properties, medicines and sanitary products, dyes, fuels, etc. Some of these examples are considered below. Living matter is, in part, matter constituted by carbon derivatives. The transformations suffered by living beings, and that we observe with the naked eye, correspond, from a submicroscopic or molecular point of view, with changes or chemical reactions of biological substances. Sugars, fats, proteins, hormones, nucleic acids, are some examples of substances, all composed of carbon, whose synthesis and degradation in the interior of living organisms is concerned with biochemistry. In this book we intend to give the student an overview of this branch of knowledge and its relationship with living beings.