One of the key messages emerging out of the recent IPCC reports is that the climate change is real, happening and will continue to happen for the foreseeable future , irrespective of what happens to future greenhouse gas emissions . The report also estimates wi th high confidence that the negative impacts on agriculture outweigh the positives which makes adaptation an urgent and pressing challenge. However, adaptation planning requires accurate information about where, when and how the impacts are going to be fel t and who will be more vulnerable. Among the regions, Africa is considered as more vulnerable due to its high dependence on agriculture for subsistence, employment and income. In Eastern Africa, agriculture accounts for 43% of GDP and contributes to more than 80% employment (Omano et al. 20 06). Within Africa, Eastern Africa is one of the most vulnerable regions due to its high dependence on rain - fed agriculture for subsistence, employment and income. The region experiences high variability in rainfall (Webster et al., 1999, Hastenrath et al. , 2007) which has a direct bearing on the performance of agriculture. Generally the region experiences prolonged and highly destructive droughts covering large areas at least once every decade and more localized events even more frequently. The region reco rded severe droughts and/or famines in 1973 - 74, 1984 - 85, 1987, 1992 - 94, 1999 - 2000, 2005 - 2006 and more recently in 2010 - 11. According to UNDP (2006), a single drought event in a 12 - year period will lower GDP by 7% – 10% and increase poverty by 12% – 14%. Extrem e events, including floods and droughts, are becoming increasingly frequent and severe (IPCC 2007). Based on the analysis of data from the international Disaster Database (EM - DAT), Shongwe et al. (2009) concluded that there has been an increase in the numb er of reported disasters in the region, from an average of less than 3 events per year in the 1980s to over 7 events per year in the 1990s and 10 events per year from 2000 to 2006. The negative impacts of climate are not limited to the years with extreme c limatic conditions. Even with normal rainfall, the countries in the region do not produce enough food to meet their people’s needs. Left unmanaged, these impacts can have far - reaching consequences on the local food security, economy, and poverty. Over the past few years, climate research has contributed significantly to increased understanding of how the climate in the region is var ying on inter - annual and decadal time scales and on how the climate is changing in response to global warming and other factors . The impacts of this variability and changes in climate on various sectors including agriculture have also received considerable attention . These studies indicate that a griculture, especially the one practiced under rainfed conditions in moisture limiting environments such as semi - arid tropics , is one of the most vulnerable sectors since these are relatively warmer places and rainfall is the only source of water. There is a rapidly growing literature on vulnerability and adaptation to climatic variability and change , but most of these studies are based on assessments made using statistical and empirical models that fail to account for the full range of complex interactions and their effects on agricultural systems (Parry et al., 2004; Cline, 2007; Lobell e t al., 2008). Evidence available to date indicate s that w ith 1°C of warming, roughly 65% of current maize growing areas in Africa will experience yield losses (Lobell et al., 2011) and the average predicted production loss es by 2050 for most crops are in t he ra n ge of 10 - 25% (Schlenker and Lobell, 2010) . For developing and implementing adaptation programs, more detailed information about the impacts of climate change on various components of the smallholder farming systems such as which crops and varieties are more vulnerable and which management practices are unviable is required . This requires a comprehensive assessment using site and location specific climate and crop management information. However, s everal problems constrain such an assessment. Firstly, downscaled local level climate change projections that are required to make such assessments are not readily available . While climate models provide various scenarios with high levels of confidence at global and sub - regional level, there are challenges in downscaling them to local level (IPCC, 2007) . Secondly, lack of information on the sensitivity of smallholder agricultural systems to changes in climate . Though process based crop simulation models can serve as important tools to make a more realistic assessment of impacts of climate variability and change on agricultural systems, application of the same is limited to few location specific studies mainly because of the intensive data requirements and practical limitations including capaci ty to calibrate, validate and perform detailed analyses. Thirdly, there is scarcity of information on how the impacts of climate change on the production and productivity of agriculture translate into economic impacts including food security at household a nd national levels. This assessment is aimed at developing more accurate information on how the projected changes in climate impact the productivity and profitability of agricultural systems that are widely adopted by smallholder farmers in Eastern Africa using the protocols and methods developed by Agricultural Model Intercomparision and Improvement Project (AgMIP) (Rosenzweig et al., 2013) . One key aspect of this assessment is the attention paid to captur e the complexity and diversity that exists in the s mallholder farm ing systems including the different ways in which th e system is managed. The study is an attempt to make a comprehensive assessment of climate change on crop growth and performance under conditions that interactions as well as related economic impacts by integrat ing state of the art downscal ed climate scenarios with crop and economic models. Th e assessment was carried out in contrasting agro - ecological zones spread over the four major countries in eastern Africa – Ethiopia, Keny a, Tanzania and Uganda. This report summarizes the findings that include trends and changes in the observed and downscaled climate scenarios, quantified information on impacts of these trends and changes on performance of maize under a range of environment al and management conditions, implication of these changes in crop performance on in come, poverty and food security of smallholder farmers and potential adaptation strategies that can assist smallholder farmers in minimizing negative impacts .AgMIP