Although numerous studies of the New Zealand Parliament have characterised MPs and their parties as exhibiting a high degree of discipline and cohesiveness in their legislative behaviour, none have provided more than a partial description of the factors thought to underly this situation as an institutional norm. Accordingly, the present study investigated the structural, behavioural and attitudinal aspects of NZ party loyalty and legislative cohesion, employing data derived from in-depth interviews with 41 current Members of Parliament. The institutional development of the two-party system in New Zealand was analysed and its effects on members' voting behaviour denoted.Scrutiny of division lists for the period 1936-1985 showed party votes to comprise some 95% of all divisions, while dissenting votes accounted for only a mere 1,35% of legislative business. Moreover, the degree of cohesion apparent in ordinary votes was reflected even in non-party, free votes on various "issues of conscience". Party discipline was however, found to be as much a consequence of the mutual agreement of legislative participants as it was the product of formal structures and mechanisms of coercion. Members' voting behaviour was observed to be both mirrored in and derived from a broad normative consensus of social expectations among MPs, expressed in the form of widely acknowledged legislative "rules of the game". Analysis of the dominant rules of the game, party loyalty and cohesion, revealed a high degree of normative structure and consensus among the responses of the MPs surveyed, regardless of party affiliation or length of legislative tenure, suggesting an effective process of institutional socialization. Finally, the study investigated the degree to which these normative expectations were adopted by individual MPs and reflected in their conceptions of legislative and representative roles. Here, despite the formal constraints on its expression, and the behavioural record of MPs themselves, the orientations of the members surveyed revealed a significant preference for the traditional "Burkean" role of independent trustee, even in situations of direct conflict with their constituents or parliamentary parties. The conjunction of a se 1 f ascr i bed independent s t y 1 e of representation with the near-uniformity of legislative voting behaviour was deemed to derive from two major sources; first, the attractiveness of this category to the self images of the MPs surveyed and second, its suitability to a state of party loyalty founded primarily on the self discipline of members themselves.