Public finance economists have been concerned with the HTT sector for a long time, but the research on this subject has not generally taken a comprehensive view. Most analysts have concentrated on a particular piece of the story. This contribution is attempted to pull many of these pieces together. In this summary paper, I draw on research in this area, and from the papers in this volume, to expand the discussion of four questions: (a) Who are the hard-to-tax? (b) What are the implications of not taxing this sector? (c) Can we measure the impact of the HTT sector tax on revenue performance? and (d) Is the tax administration system in the typical developing economy capable of reaching this segment of the population? The focus in this paper is mostly on the developing and transition economies.