This paper presents an interaction taxonomy for classifying and identifying requirement interactions in software systems. The proposed taxonomy is in the form of a four-layered pyramid that defines 6 Main Interaction Categories in the first layer, 17 Interaction Subcategories in the second layer, 29 Interaction Types in the third layer, and 29 Interaction Scenarios in the fourth layer. Each interaction scenario has a corresponding interaction detection guideline that describes how the interaction can be detected. The proposed interaction taxonomy was compared to other existing taxonomies in the literature and was not only able to address all the issues in those taxonomies, but also contained many other interaction types. The proposed interaction taxonomy serves as the first domain-independent requirement interactions taxonomy. It provides a detailed description of when two requirements interact.