The histoty of halftoning technology is presented as revealed in the U.S. patent literature, with emphasis on clustered dot halftoning. With the goal of gaining insight into current trends in halftoning, I have partitioned the history into four eras, and have categorized halftoning patents by their "scores" on a checklist of five factors that can influence the decision to turn on a microdot to construct a halftone dot. I have learned these lessons: First, both of the two major halftoning technologies have their origins in early work. The 19th century work on classical screening underlying today's electronic clustered dot halftoning is perhaps better known than work at RCA in the 1920s underlying error diffusion. Second, digital electronic halftoning by thresholding, currently the dominant technique for clustered-dot halftoning, suffers in some respects by comparison to two of its antecedents. To overcome these problems the initially elegant machinery for halftoning by thresholding has been encumbered with inelegant modifications. Third, these problems also create an incentive for fundamental innovations. Two prominent ways of doing this are to extend the list of factors that influence the decision to turn on a microdot, or to use irregular dot locations (as is already done in the dispersed dot techniques).