The paper proposes a new approach to the spelling of compound nouns - one of the most confused areas of Russian orthography. These nouns are a source of difficulties both for orthographic dictionaries and prescriptive manuals. The traditional spelling of these nouns is based on the distinction of compond words and appositive noun combinations. The distinction is too fine for ordinary users. A different method of dealing with the problem is proposed in the article; it takes into account various formal features of Russian compounds. On the basis of formal criteria, lexical material is divided into two classes: the one in which the spelling is governed by simple formal rules, and the one in which the words must be codified individually in the dictionary.