Taxation equity may be classified into horizontal equity, where people who are in the same economic position should be taxed the same, and vertical equity, where those who differ economically should be treated differently. In the New Zealand income tax, the vertical equity norm has primarily been achieved by progressive tax rates, and by family-friendly adjustments. Given that the income tax intentionally discriminates between taxpayers on the basis of taxpayer-specific characteristics such as income level and domestic situation, the question arises as to how the New Zealand income tax in its successive manifestations has been justified as fair; that is, what vertical equity in the New Zealand income tax looked like and how it was justified. This thesis considers the practice of the New Zealand income tax since its introduction in 1891 until 1984. By illuminating an employee’s lived experience of the income tax, it illustrates what taxation fairness actually looked like in practice, and contrasts this with the rhetoric of those responsible for the tax. It concludes that the reality of external events, rather than the rhetoric of taxation fairness, appears to have been the main driver of taxation practice. By focusing attention on the experience of the taxpayer, rather than merely on aggregated taxation data, legislative provisions or political discussion, the thesis permits the political rhetoric or fairness to be assessed against the fiscal impact on personal taxpayers. The thesis commences by reviewing certain influences on New Zealand income tax thought: from religion, antiquity, and more particularly from certain key British philosophers. It finds that despite their importance, these do not provide a clear direction for taxation policy. The thesis then shifts from philosophical discussions of what constitutes a fair tax to look at what the income tax actually looked like in the case of a wage or salary earner. It adopts an inductive approach by calculating the effect of the income tax legislation on employees at three income levels and in three domestic situations. The resulting nine cases demonstrate how taxpayers were distinguished for the purposes of vertical equity. Returning to the sources, this thesis then reviews contemporary Parliamentary Debates and Reports for evidence of how Parliament justified the practice of vertical equity in the income tax. Despite frequent appeals to fairness or equity, no clear basis was found. Rather, significant changes to the income tax, and thus to the practice of vertical equity, largely reflected pragmatic responses to political or economic events. Yet once such crises had passed, the income tax, and vertical equity in that tax, did not revert to the pre-crisis shape, but rather conformed to a new paradigm.