This thesis examines the policies New Zealand political parties have emphasised in their key policy statements, the ideological dimensions of party competition, how the political agenda has changed over time, and whether parties have acted in ways compatible with responsible party government and pluralist theories of democracy. These central political debates are studied using all the election programmes issued by the main New Zealand political parties between 1911 and 1996. Content analysis results for the 1911-1996 period reveal enduring differences between left and right-wing parties on economic, foreign policy and some conservative themes. While some ‘new politics’ issues such as the environment and culture have become much more important over time, the data confirms that other new politics issues such as freedom and democracy have been on New Zealand’s political agenda for most of the twentieth century. When charted on a left-right dimension, parties’ positions were largely as expected. The main left and right-wing parties have only crossed over once, and then only fractionally on the economic policy dimension. Contrary to theoretical expectations right-wing parties have often taken very moderate positions on the new politics-old politics dimension, although left-wing parties have usually been more supportive of new politics policies than right-wing parties. Differences between Labour and the main right-wing parties have usually been larger on economic than on new politics issues. However, between 1972 and 1990 differences between Labour and National on new politics issues were much larger than on economic themes. In their programmes parties have usually campaigned in a manner encouraging rational voting, and have taken relatively similar positions on potentially divisive ethnic policy issues. There is one obvious case of agenda setting: the main parties have kept the most morally contentious issues out of party politics. The enduring policy differences between the main parties will have made it easier for less well informed voters to vote in a rational manner. Party movement results indicate that only during the 1980s were National’s and Labour’s manifestos a poor guide to their subsequent policy direction. Policy implementation results for New Zealand using Klingemann, Hofferbert and Budge’s methodology showed high implementation rates by international standards over the 1946-1994 period. Often the manifestos of opposition parties were positively associated with government expenditure trends. This shows that parties’ commitment to mandate theory has been qualified by their support for pluralist norms of interest group consultation. The results indicated that between the early 1980s and 1994 the relationship between manifesto emphases and government expenditure for transfers and health has deteriorated. In other areas policy implementation rates remained high, indicating that politicians often still behaved in ways compatible with the principles of responsible party government. The regression equations Klingemann, Hofferbert and Budge use to calculate policy implementation were also reformulated to produce better and theoretically stronger results.