|The economic structure and household livelihood of Mongolia have been experiencing dramatic changes driven by both the socio-economic transition and the climate change in the past decades. This dissertation investigated the changes of population, livestock and cropland, and more importantly, the drivers of changing society and climate. Chapters 1 and 2 focused on population and migration. Population in Mongolia had increased from 2.1 million in 1990 to 2.9 million 2017, and dramatic re-distribution had also been taking place primarily by migration, which had been largely replacing nomadic movement. Urbanization accounted for over 80% of all migrations, mostly into Ulaanbaatar, where 70% of recent population growth was from migration. While relative wage ratio and job opportunity have been the most important drivers of migration and urbanization although demographic factors and climate matter too. Chapter 3 focused on livestock, which has been most essential to the Mongolian society and culture. I have investigated on the pastoral activities through examination of the behaviors of self-consumption, sale and the stock left for the future of the livestock using the Two-Stage Dynamic Model. The results revealed the pastoralists remain largely in the subsistence economy stage, but did respond to market factors such as prices, and debt to maximize the economic value of their livestock and their utilities. Chapter 4 focused on cropland, which has experienced significant increase in recent decades. A random effect semi-log model was applied to evaluate how socioeconomic and climate factors drive the dynamics. The relative wage, commodity prices, and policy were found significant roles on cropland expansion. Interestingly, cropland expansion was found not at the expense of livestock production. By integration the population, livestock and cropland tempo-spatially of the 4 chapters, I believed this dissertation would help us better understand and capture the essentials of the Coupled Nature and Human System (CNHS) of Mongolia.