Here I provide an overview of the concepts of ethnicity and industrialization. I first define ethnic groups as descent-based groups and show how vertical ethnic change can take place, both through the consolidation of smaller ethnic groups into larger ones as well as assimilation into a national identity. The chapter also discusses why the book focusses on what I call vertical ethnic change instead of horizontal ethnic change, namely because the former is far more prevalent than the latter. I then provide a similar overview of the concept of industrialization, by focussing on how industrialization has historically involved a shift in the focus of the economy from rural agriculture to urban employment and from land to labour as the predominant factor of production. I justify my use of carbon emissions as my predominant cross-national quantitative measure of industrialization and my use of urbanization as my main proxy for industrialization for regions or communities within countries.