The sustainability of livestock farming systems (LFS) in relation to global concerns about climate change, population dynamics and the quality of the agro-ecosystem services that are provided to society and their trade-offs has become a fundamental issue for public and scientific debate. However, LFS differ widely in terms of the use of resources, degree of intensification, species and orientation of production, local/regional socio-economic and market context, cultural roles, etc. Therefore, we need to disaggregate livestock farming systems when analysing any aspect of sustainability. This paper discusses low-input pasture-based farming systems (meat sheep and beef cattle) located in mountainous and other less favoured areas of the European Mediterranean basin. We first describe their recent evolution in terms of the level of intensification and structural, economic, social and environmental factors at the farm level, paying special attention to critical points of sustainability. Despite the diversity encountered, there are some common factors that threaten their future, such as an excessive dependency on premiums, the lack of generational turnover due to a number of increasingly influential social factors and a continuous process of abandonment of large marginal areas and concentration in more favourable areas. Next, we depict some relevant synergies and trade-offs between a number of factors that we have previously described, taking into account the wider socio-economic environment in which farms operate. Pasture-based LFS can satisfy societal demands (for public goods such as landscape and biodiversity or ethical concerns about food production) and are less vulnerable to market changes. However, they are not paid for the environmental services they deliver, they suffer displacement by other economic activities, and they are very sensitive to climate change scenarios. We also point out a number of options for designing and implementing more sustainable pasture-based LFS under very uncertain circumstances; the concepts of resilience, adaptive capacity and self-sufficiency are discussed within this context. Finally, we summarise some areas for future research: -valuation and integration of positive externalities of pasture-based LFS in an analytical sustainability frameworks and management tools, -assessment of the diversity of systems, the impact they generate and the public goods they deliver, -analysis of complex relationships between intensification of production, dependence on off-farm/on-farm inputs, productivity and working conditions, -consideration of the social factors that determine continuity and working conditions, -and the necessity of performing dynamic studies that allow the understanding and anticipation of change.