Are all issues subject to the same attention from organized interests? If not, why not? This article utilizes data on organized interest mobilization in Scottish public policy to examine the pattern of engagement by policy participants across a large number of policy issues. It finds a heavily skewed pattern of mobilization: Most issues attract little attention, while a few issues account for the majority of attention (they are “bandwagons”). This resembles the findings of Baumgartner and Leech, based on U.S. lobby data. Replication outside the United States supports the claim that this is a general pattern in public policy systems. But what explains such a pattern? After scrutinizing the “size and scope” approach, this article proposes that positive feedback mechanisms are catalyzing cascades of mobilization. Several agents are identified as facilitating cascades in the data: keystone groups, the media, civil servants, and campaign groups.