The International Union of Pure and Applied Chemistry (IUPAC) is an international non-governmental organization whose purpose is to promote the development of the chemical sciences worldwide and to contribute to the applications of chemistry for the benefit of humanity. One of the many tasks of IUPAC is to create a common chemical language by developing rules according to which each chemical entity is given a word (or series of words) that is unique to that compound and expresses at least its empirical formula and, if possible, its most important structural features. The idea is that these rules should be used as a basis for developing the corresponding nomenclatures in different languages. The first IUPAC "Nomenclature of Inorganic Chemistry" was published in 1957. It was translated, adapted to the Bulgarian language, and published in Bulgaria in 1964. In the meantime, the Nomenclature has been expanded and supplemented, which is reflected in the new editions of IUPAC published in 1971, 1990, 2000, and 2005. The "Nomenclature of Inorganic Chemistry. IUPAC Recommendations 2005" presented to the Bulgarian reader is an adapted translation of the English edition, with the final version of the translation approved and accepted for publication by the Scientific Council on General and Inorganic Chemistry at the Bulgarian Academy of Sciences.