Illegal physical development is an urbanization problem, so to discover the reasons behind the uncontrolled and illegal development; social, economic and political determinants such as industrialization, migration and urbanization processes should be analyzed. Therefore, to understand the process of illegal physical development, background of the phenomenon is discussed. Informal building samples from third world cities, from Turkish cities and from Izmir are given to present different variations for comparison. Policies, laws, regulations, applications and institutions involved...