Climate change in India may pose additional stresses on ecological and socio-economic systems that already face tremendous pressures from rapid urbanization, industrialization and economic development. Self-sufficiency in Indian food grain production and its sustainability is in ambiguity due to climate variability and change that occurred in the recent past. Impact of climate change on agriculture will be one of the major deciding factors influencing the future food security of mankind on the earth. To understand and address this issue, a study was carried out during at Agro Climate Research Centre, Tamil Nadu Agricultural University, Coimbatore, to assess the impact of climate change on Agriculture over Tamil Nadu by coupling PRECIS Regional Climate Model and DSSAT crop simulation model. This book is a preliminary work towards exploring the possibility of utilizing downscaled data for crop simulation modeling for impact assessment. Hence, this book will serve as a reference work for future research on integrating climate and crop models for agricultural impact assessment.