The purpose of this study was to make a tentative approach to explore the use of categories by customers of a Swedish online grocery store. The study tried to detect factors that could affect the usage of categories and the effect they can have on the behavior of customers. The store's categories were divided into traditional and mixed types and their purposes described. The study also explored the emergence of impulse purchases when using different categories and if the usage of mixed categories can affect customers to buy things they had not planned for. In order to explore this 9 participants participated in a study with a think-aloud observation and interviews at the end of every observation session. The study was conducted on a small scale and results can therefore not be generalized. Findings showed that the impact of categories alone is hard to study and that you need to take many other factors into consideration when analyzing the results. Such as the type of purchase and its purpose, the day of the week, and the labeling of the category. The results indicate that users are aware of the stores' marketing tactics of mixed categories and often make an effort not to be exposed to them to avoid impulse purchases.