This paper explores temporal variation in partisan effects on social spending growth in OECD countries over the period . We argue that partisan effects are jointly conditioned by globalization and the mobilizational capacity of organized labour. We present three main empirical findings. First, we show that partisan effects increased from the mid-1970s to the late 1980s and then disappeared in the 1990s. Second, we show that partisan effects rose with globalization in the 1970s and early 1980s, a period characterized by rising labour strength in many OECD countries, but this is not true for the post-1990 period, characterized by declining labour strength. Third, we show that globalization was associated with declining partisan effects in countries that experienced union decline in the 1980s and 1990s, but it was associated with rising partisan effects in countries in which unions remained strong.Keywords: political economy, welfare state, globalization, trade unions JEL classification: I38 government policy, provision and effects of welfare programsThe idea that parties of the Left and the Right cater to the distributive interests of their core constituencies and therefore pursue different macroeconomic and social policies has inspired a great deal of research in comparative political economy. As Keech (1995, p. 66) noted some time ago, the literature on partisanship and macroeconomic policy in the USA typically assumes that 'party differences regarding goals have remained fixed or constant' . This assumption characterizes much of the comparative literature as well, but a number of scholars, notably Pierson (1996Pierson ( , 2001a and Huber and Stephens (2001a, b), have argued that government partisanship became less salient to social policy in the course of the 1980s and the 1990s. Against the decline-of-partisanship thesis, Korpi and Palme (2003) and Allan and Scruggs (2004) remained an important determinant of the benefits provided by social insurance schemes in the 1980s and 1990s. We seek to contribute to this debate about inter-temporal variation in the effects of government partisanship in the realm of social policy and, in so doing, to advance the broader agenda suggested by Keech, i.e. to explore the conditions that affect the goals pursued by parties.The question of changes in the salience of government partisanship must not be conflated with the question of shifts in the centre of political gravity. For our purposes, the critical question is not whether Left-leaning governments are less prone to engage in welfare-state expansion today than they were 20 or 30 years ago, but rather whether the policies of Left-leaning and Right-leaning governments have converged or diverged. There is lots of evidence to suggest that the centre of political gravity moved to the Right in most OECD countries in the 1980s and 1990s. To the extent that Right parties moved farther in a rightward direction than Left parties, however, we would observe an increase in partisan differences as well as a rightward shift of all partie...