Green job growth over the next 5-10 years is expected to be highest in the building and transportation sectors. Higher energy consumption, rising greenhouse gas emissions, road congestion and deteriorating water quality are the negative externalities that have come with urban growth. Many metropolitan regions across the OECD have turned their attention to the concept of green growth as a means of increasing economic competitiveness through addressing environmental challenges (Box 1.1). What do we mean by urban green growth?