This ENCYCLOPAEDIA OF MATHEMATICS aims to be a reference work for all parts of mathema- tics. It is a translation with updates and editorial comments of the Soviet Mathematical Encyclo- paedia published by ‘Soviet Encyclopaedia Publishing House’ in five volumes in 1977 – 1985. The annotated translation consists of ten volumes including a special index volume. There are three kinds of articles in this ENCYCLOPAEDIA. First of all there are survey-type articles dealing with the various main directions in mathematics (where a rather fine subdivision has been used). The main requirement for these articles has been that they should give a reason- ably complete up-to-date account of the current state of affairs in these areas and that they should be maximally accessible. On the whole, these articles should be understandable to mathematics students in their first specialization years, to graduates from other mathematical areas and, depending on the specific subject, to specialists in other domains of science, en- gineers and teachers of mathematics. These articles treat their material at a fairly general level and aim to give an idea of the kind of problems, techniques and concepts involved in the area in question. They also contain background and motivation rather than precise statements of pre- cise theorems with detailed definitions and technical details on how to carry out proofs and con- structions.