Livestock farming is facing major challenges at a global level due to increasing uncertainty in markets, policies, socio-cultural trends, and the environment. One of the hot topics in research and policy design is to reconcile the sometimes conflicting objectives of delivering both animal products and environmental services. On mountain pastures in particular, adequately conducted livestock can be a tool for the efficient management of large areas of high natural value. At the same time, it can sustain a viable economic activity and provide differentiated products that fulfill societal demands for quality and environmentally-friendly production. Optimizing these aspects requires a multidisciplinary approach, combining research and development on ecology, animal, plant, social and environmental issues. This publication compiles 60 articles of the contributions presented at the 19th Meeting of the FAO-CIHEAM Mountain Pastures Subnetwork, held in Zaragoza (Spain) in 2016: “Mountain pastures and livestock farming facing uncertainty: environmental, technical and socio-economic challenges”. Over 90 researchers and technicians involved in research and development activities on mountain pastures participated in the Meeting, structured around four specific scientific topics: 1) Pathways towards mountain farming system sustainability: assessment methods and case studies ; 2) Livestock on mountain pastures: animal performance and quality products ; 3) Animal-Pasture interactions in mountain areas: bottlenecks and opportunities in biodiversity management and forage production ; 4) Mountain pastures and society: biophysical, economic and socio-cultural valuation of ecosystem services.