There are various types of reform, each with its own assumptions, goals, and constituencies, reflecting broader political conflicts over criminal justice issues. The various reform efforts interact with one another to stimulate parallel efforts in some cases and opposing efforts in other cases. Reform efforts are constrained by the external social and political environment. In some cases, the reform impulse originates from external sources. At other times, external sources support and shape reform movements, or they may obstruct or blunt internally generated reform. The impact of particular reform efforts is ambiguous. Attempted reforms are never completely successful; for example, the prisoner's rights movement has enormously impacted American corrections, but the full dimensions of the impact have yet to be analyzed. Any assessment of a reform's impact must recognize the typically complex and multidimensional aspects of criminal justice reforms throughout history. 59 references and 5 footnotes.