A method for the description of the hierarchical structure of two-dimensional pictures is proposed. The model is called picture-processing grammar. It can be regarded as an extension of phrase-structure grammars to the two-dimensional case. A picture analysis program is described. It accepts picture-processing grammar in tabular form and processes pictures using that grammar. Experiments have been performed to analyze hand-written numerals, mathematical expressions and line drawings. Some practical applications are discussed. © 1971 American Elsevier Publishing Company, Inc.