Three studies examined the role of prior consideration of categories on a brainstorming task. Participants were asked to generate abstract categories before they brainstormed either in groups or individually in Experiment 1. It was expected that generating categories before ideation would be beneficial. However, it was found that category generation harmed the group ideation process. Prior category generation reduced clustering of ideas within categories for groups, which might have led to a decrease in productivity. The last two experiments examined whether groups would benefit by brainstorming one category at a time because this might increase clustering. It was found that sequential category brainstorming helped increase productivity during the ideation process and increased clustering. These studies demonstrate that a prior categorization phase can facilitate subsequent brainstorming because it enhances sub sequent clustering of ideas within categories.