Combinatorics belongs to those areas of mathematics having experienced a most impressive growth in recent years. This growth has been fuelled in large part by the increasing importance of computers， the needs of computer science and demands from applications where discrete models play more and more important roles. But also more classical branches of mathematics have come to recognizee that combinatorial structures are essential components of many mathematical theories.
　　Despite the dynamic state of this development， we feel that the time is ripe for summarizing the current status of the field and for surveying those major results that in our opinion will be of long-term importance. We approached leading experts in all areas of combinatorics to write chapters for this Handbook. The response was overwhelmingly enthusiastic and the result is what you see here.