It has been possible to present in this short review a rather circumscribed picture of the field concerning the utilization of energy for the transport of substances. I have specifically considered metabolic energy and to a large degree have emphasized “bulk transport” and sodium transport. One important part of the field, the transport of non-electrolytes, has been omitted in this essay. “Uphill” transport of sugars, for example, is well known to require metabolic energy and certainly merits discussion in an article of this kind. Some idea of matters unwillingly or unwittingly slighted by this author can be derived from any one of numerous excellent recent reviews, e.g. that of the Hokins . The choices of topic that have been made stem from the specific interests of the author, and the major emphasis of the literature. The viewpoint of this essay also stems in marked degree from the atmosphere, discussion and general sense of exploration of the Frascati meeting. The important objective has been to emphasize the nature ot information already achieved, and to point up a few of the matters that should yield to probing in the next few years — especially the matter of the detailed mechanisms of ATP involvement in transport processes.