Despite the scepticism that increasingly surrounds their role and standing in contemporary democracies, scholarly interest in political parties continues unabated. But this interest is also proving uneven, with relatively little attention now being given to the study of party systems. More specifically, the level of theoretical interest in party systems remains limited, with almost no substantial innovations being made since the publication of Sartori's classic work of 1976. In this article, we seek to redress some of this neglect by identifying the relevant parameters that can be used in the definition of party systems and, possibly, in the explanation of party system change. We then go on to look at the minimum defining characteristics of a system of parties ( as opposed to a set of parties) before finally arguing that party systems are best understood as multidimensional phenomena in which we identify and discuss the implications of three types of division - vertical, horizontal and functional.
