This paper reviews the major environmental and non-environmental drivers of migration in the mountainous regions of the developing world. Mountains are highly diverse in terms of their physical, socioeconomic and political environments. Mountain environments are highly fragile and their inhabitants are exposed to both environmental and non-environmental stressors, which are interlinked and have serious implications for mountain livelihoods. The combination of multiple agricultural and non-agricultural income sources is a characteristic of mountain people’s livelihood systems. Migration is not a recent phenomenon, but has been a traditional source of non-farm income to varying degrees. This review finds that migration behaviour is influenced by a combination of environmental (floods, flash floods, landslides, droughts and land degradation) and non-environmental (economic, demographic, social and political) drivers. As the decision to migrate or not is ultimately an individual one, it is methodologically challenging to single out any single driver as significant – a fact well reflected in the available literature. The inter-relationship between the dynamics of the factors triggering migration and migration dynamics has been rarely explored. In particular, studies concentrating on migration in the mountainous regions of the developing world are few.