An Extension of ALGOL 60 B. Buchberger Communications of the Joint Institute for Nuclear Research, Dubna, Soviet Union, No E5-5787, March 1971, 13 pages. ABSTRACT: We define an extension of ALGOL 60 by which, within the language, it is possible to formulate programs that change themselves. We define the extension formally in the Vienna Definition language and show the correctness of the extension. Extensions of this kind are important for being able to formulate learning programs and pre-processing programs in symbolic computation in procedural languages.