Book excerpt: The multiset, as a set with multiplicities associated with its elements in the form of natural numbers, is a notation which has appeared again and again in various areas of mathematics and computer science. As a data structure, multisets stand in-between strings/lists, where a linear ordering of symbols/items is present, and sets, where no ordering and no multiplicity is considered. This book presents a selection of thoroughly reviewed revised full papers contributed to a workshop on multisets held in Curtea de Arges, Romania in August 2000 together with especially commissioned papers. All in all, the book assesses the state of the art of the notion of multisets, the mathematical background, and the computer science and molecular computing relevance.