The format of this mograph is three essays, which we arrived at after spending a year writing over one hundred pages of what we even- tually realized was a tedious reworking of old material. So we started over determined to write something new. At first we thought this approach might t work as a coherent mo- graph, which is why we chose the essay format rather than chapters. As it turns out, there is a common thread-namely the directional distance function, which also gave us our title. As you shall see, the directional distance function includes traditional distance functions and efficiency measures as special cases providing a unifying framework for existing productivity and efficiency measures. It is also flexible eugh to open up new areas in productivity and efficiency analysis such as environmen- tal and aggregation issues. That we did t see this earlier is humbling; a student at a recent conference raised his hand and asked 'Why didn't you start with the directional distance function in the first place? In- deed. This manuscript is intended to make up for our earlier oversights. This mograph contains papers coauthored with Wen-Fu Lee and Osman Zaim and one paper written by two former students, Hiroyuki Fukuyama and Bill Weber. We thank them for their contributions. An- other former student, Jim Logan (Logi) read and critiqued the manu- script for which we are grateful.