The textbook "Dietotherapy" is an original work that will give students and the general public a clear, new, scientifically research-based insight into diet therapy and all the areas it covers. The work includes all significant clinical conditions that people who are in direct contact with people who need a special diet face every day. From the text, you will get an insight into how ubiquitous diet therapy really is. It covers everything from maintaining the state of health, improving it, or as support for medical therapy and treatment. When we talk about diet therapy, we usually mean patients, that is, people who suffer from various diseases and are placed in hospitals. It is important to emphasize that, in addition to this most significant and critical group, diet therapy also covers people who are in home care, are in specialized institutions (e.g. homes for the elderly and infirm), or are otherwise healthy but require special care due to specific physiological conditions that is necessary to satisfy (e.g. premature babies, pregnant women, women in menopause). Considering the wide range of areas covered, this material will be of great use to anyone who ever encounters the demands of diet therapy. Probably the greatest feature of the presented materials lies in the fact that all the areas covered are covered in great detail according to the latest scientific research, and everything is related to today's way of life. Some of these conditions (cardiovascular diseases, cancers, type 2 diabetes, obesity) represent the main causes of mortality, both in Croatia and in the world. On the other hand, there are diseases of the gastrointestinal system, kidney diseases, lung diseases, deficiency diseases and diseases related to aging; conditions that significantly affect the very outcomes of the applied medical therapy, as well as the quality of life, which today represents primacy in an increasingly aging population.