In 1781, the " States of Languedoc " , a French province, recruited at the University of Montpellier chemist Jean-Antoine Chaptal to develop the chemical industry in this region. The idea of using scientific and technological innovation to promote local economic development is not new. This idea has generated numerous policies since Chaptal. Some rely on the development of universities capable of training a skilled workforce and to provide scientific support to industry. Others give more purpose to promote the creation of new firms or the networking of existing ones. They do so in ways very different, from technology parks to policy of "clusters" funding projects that involve local collaborations. Finally, more recently, policies based on the theory of "creative class" have sought to attract not companies but persons whose profession is related to innovation activities, that they are technical, economic or cultural. This text present a review of these policies, from a series of studies conducted in France and Europe. The text will not seek to make a survey of public policies analysis, but rather to give a view based on some field studies. The effect of public policies can be of three types: non-existent, simple maintenance of existing balances, changes in these balances. With regard to the policies of local development based on innovation, if the first two kinds are widespread, the third is much rarer. This is partly because many policies are based on misconceptions about the mobility of firms and individuals (business parks, creative class), or the effect of simple spatial proximity of linking people or companies (effect "cafeteria" or "coffee machine"). The search for quick fixes, inexpensive and visible, favors policies which are usually ineffective.