As an important data mining and knowledge discovery task, association rule mining searches for implicit, previously unknown, and potentially useful pieces of information—in the form of rules revealing associative relationships—that are embedded in the data. In general, the association rule mining process comprises two key steps. The first key step, which mines frequent patterns (i.e., frequently occurring sets of items) from data, is more computationally intensive than the second key step of using the mined frequent patterns to form association rules. In the early days, many developed algorithms mined frequent patterns from traditional transaction databases of precise data such as shopping market basket data, in which the contents of databases are known. However, we are living in an uncertain world, in which uncertain data can be found almost everywhere. Hence, in recent years, researchers have paid more attention to frequent pattern mining from probabilistic databases of uncertain data. In this paper, we review recent algorithmic development on mining uncertain data in these probabilistic databases for frequent patterns. © 2011 John Wiley & Sons, Inc. WIREs Data Mining Knowl Discov 2011 1 316–329 DOI: 10.1002/widm.31