Manyareas of mass spectrometry are exhibiting amazing rates of growth. In the preparation of this review, which covers the available literature through 1965, over 5000 references were collected which had appeared since the last biennial review by Reese and Harllee (895). For the drastic reduction of this number necessary for the review, a definition of the field of analytical mass spectrometry has been formulated with some rather arbitrary boundaries. The important field of