https://dzone.com/articles/apache-flink-1Most teams working with Apache Flink think about stream processing: filter events, aggregate values, enrich records, join streams. This covers the majority of real-time data problems. But there is a specific class of problems that stream processing handles poorly: detecting meaningful sequences of events across time. Did this specific chain of things happen, in this order, within this time window? Complex event processing (CEP) is the tool designed for exactly this, and it works fundamentally differently from stream processing.CEP is a built-in capability of Apache Flink, available as open source and deployable at scales the old proprietary platforms could never reach. Yet it remains underused and misunderstood. This article is a practical guide to what CEP is, when to use it, how Flink implements it, and where it fits in modern data architectures, including agentic AI, which is covered in depth in the companion article.