The partition of Ireland into two separate political jurisdictions in 1922 reflected the very different economic trajectories pursued by the two parts of the island during the course of the nineteenth century. Since then, both regional economies have experienced several changes of direction in their respective development paths. For a brief period in the 1960s, similar development policies produced a pronounced movement towards convergence in the economic structures of the two regions. Since then, however, the trend has been toward renewed divergence, so that at the beginning of the 21st century the economy of the Republic of Ireland appears much more vibrant than that in Northern Ireland—a remarkable reversal of the position that obtained at the time of partition. This chapter traces the historic evolution of the two Irish economies, placing this evolution in the context of general concepts and models derived from the literature on economic development. Despite the different and varying development trajectories followed by the two economies, these trajectories can both be readily accommodated within a generalized core-periphery development model. At the same time, there have been exceptional elements in the developmental experiences of the two economies, which have conferred unique features on each