Wheat production environments in Ethiopia are highly heterogeneous with respect to natural resource characteristics, cropping systems, biotic and abiotic constraints. This paper analyses the agro-climatic resources of 20 representative wheat growing sites in the country and groups them by cluster analysis to develop homogeneous environmental groupings for wheat improvement research. The wheat growing sites are defined and clustered based on precipitation, temperature, altitude, longitude, and length of growing season. Annual precipitation decreases along a west-east axis, ranging from 1784 to 585 mm. The major feature of the precipitation pattern is its seasonality with distinct dry and rainy seasons. Generally, rainy season duration extends from 2.5 to 6.5 months. In the western, central and northern parts of the country, rainfall distribution is generally monomodal. In the eastern part of the country (i.e., 39.4 to 42.5° E) the distribution is bimodal, resulting in two cropping seasons, viz. "belg" (short) and "meher" (main). Of the parameters studied, annual and main season precipitation, and length and end of growing period were negatively correlated with longitude (r = -0.73**, -0.82**, -0.64** and -0.43*). Altitude was negatively correlated only with maximum and minimum temperatures (r = -0.64** and -0.86**). Three main environmental groups (C1, Western; C2, High Altitude; C3, Eastern) and six subgroups (C1-1, C1-2, C2, C3-1, C3-2, C3-3) were identified in the cluster analysis. Such clustering into homogeneous environmental groups should assist the national wheat improvement programme in making decisions about test site selection and proper targeting of released varieties.