After a brief historical survey starting around 1930, the article discusses some of the main new concepts used in development models. Thus, the Domar- Harrod principle, planning in stages input-output, and two-gap models are discussed. From national models we have now attained a point of world models. The newest developments are characterized by the introduction of income distribution variables, the informal sector, appropriate technologies and environ. mental variable.. New uses made of mode1J recognize the existence of more than one policy maker. or alternative groups in power as well as ”interactive multiple goal planning”.