The fact that the world's cities are getting more and more crowded is a well-documented demographic fact. Cities such as Tokyo, Sao Paolo, Bombay and Shanghai are now considered "mega-cities", reflecting their enormous size and huge populations, which in many cases is around the twenty million-mark. There are two main reasons why these and other cities are becoming so crowded: one economic and other socio-cultural. 1 Undoubtedly, the primary cause for cities becoming socrowded is economic. With a country develops, its cities become 2the engines of development. Furthermore, many jobs are available 3in these areas. Tokyo, for example, is the motor for Japan's rapid 4economic development in the 1960' s and 70' s; as a result, its population increased rapidly. People moved to Tokyo so that theycould find jobs and establish economic security themselves and 5their families. A further factor in the huge increase in urban populations isthe socio-cultural factor. Thousands of people migrating to the 6cities not only for jobs but also for educational and personnel 7reasons. The better universities are always located in big cities and this attracts tens of thousands of students every year. Thesestudents usually stay up and work in the city after they graduate. 8Moreover, young people will move to the city as if the villages and 9rural areas are often governed by custom and tradition, which they believe is an obstacle to their private freedom. In conclusion, we can say that amongst the many causesbehind urban population density, the economic or cultural are the 10most significant. People always move to the areas which provide opportunity and the freedom they desire. It is now the responsibility of municipal councils to make sure these people are housed, clothed, fed and educated.