It has always been the policy of SUBCELLULAR BIOCHEMISTRY to be flexible in the size of its articles. In some cases the author may wish to deal with a relatively narrow aspect of his subject and suggestions that he enlarge the article would not necessarily be welcomed. On the other hand, there are occasions when the topic demands a large canvas. It could be argued that the present facilities available in the biochemical literature are inadequate for those who wish to develop an argument in extenso. Short of publishing a book on the subject (a course of action that would raise all sorts of questions of marketability, presentation, etc. ), an author with an article that passes the 1- page barrier could well find great difficulty in finding an outlet for his work. We are therefore very happy to include in this volume an extensive and erudite account of electron microscopy by H. Plattner and H. P. Zingsheim. The article deals initially with all aspects of modern electron microscopy as applied to biological problems. For every basic technique used, the physical background and theory is clearly explained and extensive references are given to the various adaptations and modifications of each technique. The article is richly endowed with diagrams, tables, and sample electron micrographs and should be extremely useful both to the "cognoscenti" and to those first entering the technically demanding but nevertheless fascinating field of electron micros­ copy.