ABSTRACT This paper summarizes the preparation of climatic design conditions for the 2009 ASHRAE Handbook ?C Fundamentals. The project (a) redefined new percentiles of monthly dry bulb and wet bulb temperatures to represent ??less extreme' conditions than those used in the past@ (b) added new monthly dry bulb and wet bulb coincident temperature ranges which can be used for the derivation of daily temperature profiles@ (c) calculated heating and cooling degree-days base 50??(10?? and 65??(18.3??@ in support of various standards including ASHRAE Std. 90.1-2004@ and added parameters to accurately evaluate degree-days to any other base@ and (d) developed a new clear sky solar irradiance model@ to overcome the known limitations of the existing ASHRAE clear sky model and extend its applicability to the whole world. The most recent 25 years of climatic data (1982-2006 at the time of processing) were used to calculate the revised tables of climatic design conditions. This provides a balance between accounting for long-term trends and the sampling variation owing to year-to-year variation. Processing led to the calculation of climatic design conditions for a total of 5@564 locations worldwide.