We only need to think for a moment about surfaces and other interfaces to realise their enormous importance in everydaylife. There are numerous branches of physics, chemistry, biology, and materials science concerned wholly or largely with surfaces, and one sometimes comes across the expression ‘surface science’ Among the natural phenomena connected with surfaces which have aroused scientific interest are surface tension, surface waves, photoelectric emission, reflection, refraction, evaporation, adsorption, adhesion, thin films, detergents, catalysts, cell membranes, skin. All of these phenomena are complex, interesting, and some of them are still far from completely understood. Are surfaces important for philosophy? An epistemologist might well answer affirmatively, thinking of Quine’s "surface irritations" as the basis of our knowledge of the physical world, or Berkeley’s theory of vision, or the view that we perceive a material object in virtue of suitable causal interaction with its surfaces. But at first sight it seems that there is not much of interest for an ontologist. In his work on surfaces, especially in the book of that name, Avrum Stroll has shown to the contrary that there is much ontological interest in surfaces} Every ontologist delights in a newly discovered or hitherto neglected member of the ontological zoo: surfaces are not exactly new, but they have been neglected, and we can be grateful to Stroll for bringing them to greater prominence.