A multi-agent system is a useful approach for the complex systems. One of the important concepts of multi-agent systems is cooperativeness, or interactions. However, existing languages for implementing interactions lack expressiveness. This causes gaps between design and implementation. This paper analyzes language functionalities for implementing interactions. Furthermore, a new interaction description language IOM/T is proposed based on the findings. Interaction would become easy to implement based on design using IOM/T. Categories and Subject Descriptors D.3 [Programming Languages]: Language Constructs and Features General Terms Languages Keywords Multi-Agent System, Interaction, AUML