In this book Michel S. Laguerre argues that there exists an informal city located just beneath and in the interstices of the formal city. The metaphor is not geographical, but rather structural and hermeneutical. It is the city of behind-the-scene maneuvers, an informal ethos that everyone seems to participate in, although usually unspokenly because of the highly sensitive character (personal, sometimes unethical or perhaps illegal) of the activities carried out there that shape the formal outcome. This study further argues that informal practices which are by no means trivial constitute an important factor in the shaping of everyday life at the personal, group and institutional levels. It shows that these informal practices shape, sustain, support, undermine and influence in many different ways the flow of processes and activities of the formal system of society. It further demonstrates that, without them, the formal system would not be able to function smoothly, because they constitute an integral part of its operation. With illustrative data drawn from the American urban experience, the authors shows why and how the informal city must be seen as the hidden dimension of the formal city.