This study is a Comparative Foreign Policy (CFP) analysis of the Palestine Liberation Organization's (PLO) foreign policy behavior from 1964 through 1981. This study develops and tests a role modification model that accounts for evolutionary changes in foreign policy behavior. One of the major premises of this research is that what often appears as dramatic restructuring in foreign policy is actually the culmination of a series of modifications that transpired over an extended period of time. The model relies on a total of six independent variables as determinants of PLO foreign policy output representing multiple levels of analysis. There are a total of 12 dependent variables expressed as either foreign policy tactical roles or strategic goals. Relying on content analysis of relevant PLO documents, the role modification model demonstrates that the foreign policy output of the PLO experienced a gradual, over time change in both the means and ends of its foreign policy. The model also identifies the conditions under which any one of the independent variables is able to exclusively determine foreign policy output and which roles one can reasonably expect the PLO to exercise under a given circumstance.