This chapter evaluates new institutional economic theory and its approach to explaining economic transformation and political order. It explains the key assumptions of the ‘old’ New Institutional Economics, associated with the work of Douglass North prior to 2009. It then sets out the more recent developments within New Institutional Economics that engages more explicitly with power, in the work of Acemoglu, Robinson and North et al. The chapter evaluates the extent to which these theories can help explain Tanzania and Vietnam’s experiences of political reform and economic change over the era of high growth. The chapter argues that while the ‘new’-New Institutional Economics of development correctly identifies the importance of power in explaining economic transformation, these theories remained tied to a number of restrictive neoclassical assumptions that limits the extent to which they can illuminate processes of contemporary economic change.