Complex compounds are characteristic of all inorganic and organic chemistry. They are found in gases, liquids and solids, in animal and plant organisms. The special role of complexes is in chemical technology. The book summarizes the history of the emergence of our knowledge of complexes and coordination, "simple" and "complex" compounds, about valence. The amazing features of the complexes, the reasons and conditions for their existence and reuse can be found by reading this book, replete with illustrations and examples. The book is intended for schoolchildren, students, teachers and everyone who wants to expand their knowledge of chemistry.