In current windowing environments, individual windows are treated independently, making it difficult for users to coordinate information across multiple windows. While coordinated multi- window strategies are increasingly used in visualization and web user interfaces, designs are inflexible and haphazard. The space of such linked-window strategies is not well understood and largely unexplored. This paper presents a taxonomy of coordinations, identifies important components, and reviews example interfaces. This 2x3 taxonomy provides guidelines for designers of applications, user interface toolkits, and window managers. We hope to encourage construction of generalized, end- user programmable, robust, multiple-window coordination capabilities.