Abstract: There were many temporal data models proposed in the literature. Most of them are based on relational models. Despite their popularity as design and analysis tools for information systems, ER-based temporal data models do not draw as much attention as those based on relational models did. One reason is that most ER-based temporal data models lack underlying formalism and algebra. If a conceptual model, along with an algebra, is formally defined, we can design a query language that operates on the conceptual model, not on the implementation model. Also, it can provide a basis for a user-friendly, visual query language. In this paper, we present a temporal algebra for an ER-based temporal data model called ITDM (Integrated Temporal Data Model). We define ten algebraic operations and ten temporal aggregate operations. We also define time-series specific operations.