Psychological explanations of inmate litigation contend it reflects chronic inmate contentiousness; and a second type of explanation, termed the 'permissive judiciary' theory, locates the primary cause of increased inmate filings in the decisions of activist judges who have provided inmates with both the means and the motivation for litigation by intruding in matters best left to States. A third explanation is that the increase in inmate litigation simply reflects an increase in the Nation's prison population; and a final explanation, the 'social resistance' thesis, is that the litigation stems from particularly objectionable prison conditions. Shifting filing grounds, changing legal theories on which inmates sue, the expansion of specific inmate rights through Federal court decisions, and shifts in the rates of suits per inmate suggest that inmates are responding to singular issues that may shift periodically. These findings undermine the psychological and demographic explanations of increased inmate litigation. The data provide some support, albeit marginal, for the judicial permissiveness thesis. Data most strongly support the explanation that inmate litigation is a form of social resistance to perceived problems either in the criminal justice system or prisons. 7 tables, 38 references. (Author abstract modified)