<p><strong>New Zealand parliamentary procedure has been reformed gradually over the 80-year period between 1935 and 2015. It has moved away from its Westminster roots in some important respects, but its origins remain recognisable. This thesis studies how parliamentary procedure in New Zealand has changed and what has caused those changes in the period 1935 to 2015.</strong></p><p>Taking an interpretive approach, this project examined change from the perspective of the participants in it. The thesis drew on the model developed by James Mahoney and Kathleen Thelen in ‘A Theory of Gradual Institutional Change’ (2010), which categorises rule changes as displacement of existing rules by new ones; layering of new rules on existing ones; drift in which rules remain the same but their effect is altered; and conversion where rules are unchanged but are reinterpreted. It found that the New Zealand parliament favours change by layering and displacement, which occur in institutions where discretion to interpret rules is low. Because of a preference for written rules and regular review of procedures, there is little scope for conversion of rules or drift in their meaning. There has been a greater use of layering of new rules on existing ones since the change to the MMP electoral system, reflecting an increase in the number of veto players and the greater complexity in reaching consensus about change. Over the period of the study, detailed work of scrutiny of the executive, law-making and House management shifted from the plenary to committees. Layering was the preferred way to make changes to rules governing select committees, reflecting caution changing a part of the parliamentary machine that is well-regarded. The creation of the House business committee has been enthusiastically received and many additional responsibilities layered onto it since its inception in 1996. This reflects the general preference for layering, post-MMP, and the nature of the committee lending itself to the addition of responsibilities, rather than replacement of one role with another. While elected members are sensitive to public opinion, almost all changes to rules and practice are proposed by members or parliamentary officials. New Zealand has institutionalised regular review of its rules and takes a consensus approach to rule changes. This approach generally ensures incremental change but also makes regular review and change part of parliamentary culture. Ongoing reform is likely in light of the desire of parliamentary actors to keep the institution relevant to the public, the institutionalised review process and continued proposals for change.</p>