The effects of both external and internal airflow need to be considered during the design of buildings and other structures. Two basic approaches can be used to solve design problems associated with airflows. The first involves the use of testing scale models, which for external airflow problems is typically undertaken using wind tunnels. The second approach involves the use of computational fluid dynamic (CFD) techniques. CFD has demonstrated versatility in building design at various stages of the design process. CFD has proven to be a very useful companion to wind tunnel testing and physical measurements in solving airflow problems.