General definitions of mobbing and rioting have differed very little for more than 150 years, and practice has strengthened the tendency to use the two terms together. An important distinction between mobbing and other crimes of disorder is that the former requires a common purpose, although the precise nature of this requirement is not clear. While mobbing does not require violence, the law of concert is applied and often taken further than in the case of most other crimes. An historical review of mobbing and rioting cases reveals a shift in emphasis from important social considerations in the 19th century to use of the charge in dealing with gang fights in the 20th century. This trend has become marked in the last two decades. The report reviews public order offenses in the United States, Germany, Norway, Sweden, and the United Kingdom and then comments on undesirable features and consequences of the present law in Scotland that stem from the common-purpose and guilt-by-association doctrines. Options for reform both in judicial practice and substantive law are proposed. Questions on which consultees' views are sought are appended along with case examples.