John Lott and David Mustard launched an enormous amount of scholarly work on the effect of laws, specifically the “shall-issue” laws which enabled citizens to carry concealed handguns. Their results suggested that these laws reduce crime because simple panel data regression models for the 1977 to 1992 data period that they first analyzed provided support for the view that some or most violent crime rates fell for the 10 States that adopted “shall-issue” laws over that period. However, concerns regarding these results came to the surface. Several analysts showed that disaggregating the 1977-92 data to estimate effects on 10 individual States led to a more mixed picture with some States showing increases and other States showing decreases in crime. This chapter examines the research results of Lott and Mustard and the concern in the vulnerability of the results because the panel data model may not adequately control for unobserved or difficult-to-measure factors that influence local crime rates but change over time. The overall evidence suggests that broad and conflicting crime swings that occurred in the late 1980's and 1990's happened to correlate with the passage of “shall-issue” laws, and the panel data model seems unable to separate out the contribution of the relatively minor influence of the “shall-issue” law from the major impacts of these broad swings. Tables, figures, comments and references