Industrialisation (alternatively spelled industrialization) is the period of social and economic change that transforms a human group from an agrarian society into an industrial society. This involves an extensive re-organisation of an economy for the purpose of manufacturing. Historically industrialization is associated with increase of polluting industries heavily dependent on fossil fuels; however, with the increasing focus on sustainable development and green industrial policy practices, industrialization increasingly includes technological leapfrogging, with direct investment in more advanced, cleaner technologies.