This book is designed to aid understanding the roles of local people as active actors in the rapidly changing mountainous environments, and examines these roles from the viewpoints of livelihood security in the state of Himachal Pradesh, northern India. It consists of the following three sections; 1. the roles of changing agricultural production and changing physical environments, 2. the impacts of tree plantation in the context of income and community participation and 3. the socio-economic issues among the group of newcomers. These tasks are studied by using exploratory approach, participant observation, interviews through random and cluster sampling, land cover interpretation and secondary statistical data among villagers, local land users and officials. This book is relevant for educational uses on the issues of stating livelihood security in rapidly growing developing country.