This chapter defines the key concepts that are central to this volume: what are green jobs and green skills and what are the implications for low-carbon economies if there is not enough of either. Labour market impacts from the transition from high- to low-carbon intense production will affect all workers. However, changes will be minor for the majority, but substantial for a small number of industries and professions. The skills and training implications are threefold: i) upgrade skills sets in industries experiencing only minor adjustments; ii) gearing up educational institutions and firms to provide the new skills for new occupations and sectors that will emerge from the green economy; and iii) retraining and realigning skills in sectors that will decline as a result.