With recent advances in technology, animations and simulations are increasingly available for science education. These dynamic resources can be useful for communicating some of the critical ideas that are fundamental to chemistry; however, numerous factors contribute to their effectiveness. In this chapter, we describe our research in designing and implementing a sequence of interactive multimedia simulations on Kinetic Molecular Theory and associated topics, developed for use in high school classrooms. We first discuss the role of representations in chemistry learning, specific attributes of simulations and animations, and theoretical approaches to how people learn from multimedia resources in general and dynamic representations in particular. We then situate this theoretical discussion in practice by describing our own experience in designing, building, testing, and implementing simulations for chemistry education.