These 17 papers result from a 1983 conference held to honor Professor Mahlon Marsh Day upon his retirement from the University of Illinois. Each of the main speakers was invited to take some aspect of Day's pioneering work as a starting point: he was the first American mathematician to study normed spaces from a geometric standpoint and, for a number of years, pioneered American research on the structure of Banach spaces. The material is aimed at researchers and graduate students in functional analysis. Many of the articles are expository and are written for the reader with only a basic background in the theory of normed linear spaces.