This paper examines how the two parts of Ireland were affected by the partition of the country in 1922. It examines the post-partition evolution of living standards north and south, and patterns of trade, migration, and road and rail traffic between the two since 1922. A separate section looks at the effects of living near the border on population trends. Bearing in mind the difficulty of establishing a relevant counter- factual—what would have happened in the absence of partition—we conclude that while it is possible to discern a “partition effect”, it is smaller and less significant than is widely perceived. The evidence we present is a salutary warning against great expectations about the possible economic gains from the dismantling the barriers erected between the two parts of Ireland after 1922.