Formation, characteristics of, and applications rising doubly and multiply charged ions are reviewed in the present article. The main emphasis is on medium- to large-sized molecules, from the point-of-view of organic, physico-organic, and bioorganic mass spectrometry. Multiply charged species can be studied by all conventional mass spectrometric techniques. Those techniques and reaction types that are particularly relevant to multiply charged ions are discussed in some detail in Section III. Studies on small- to medium-sized molecules are discussed in Section N. A particularly interesting aspect, the distinction of doubly charged isomeric ions, is also treated here. Multiply charged ions of large (bio-)molecules are discussed in Section V. This area is fast expanding, mainly due to the spread of electrospray ionization. Fragmentation and conformation of multiply protonated peptides is discussed in detail.