In recent years, the computation of load and energy requirement in buildings, energy conservation studies in buildings, and the design of solar systems are not accomplished using long-term averages of weather data as inputs, but preferably with data-sets representative of the climatological features of the site that are generated for this purpose. Such data-sets are the test reference year, typical meteorological year and weather year for energy calculations. In this paper, the basis, the selection procedure and the use of each of these data-sets are discussed Also, an attempt is made to generate typical weather years for the cities of Dhahran, Riyadh, Jeddah, Khamis-Mushayt and Hail, using the standard meteorological data obtained by measurements by the Meteorology and Environmental Protection Administration.