4D CAD has been an active research area for many years. The first generation 4D toots simulated construction schedules and demonstrated the potential benefits in several case studies. Researchers tried to improve the functionality of the first generation 4D tools by adding annotations and highlighting the building elements that have problems. The future generation 4D tools are expected to include more than these. It has been envisioned that 4D models would he part of project databases in order to take decisions related with different project dimensions.