I do not remember when my interest in social norms began, but the subject has been a long-standing source of curiosity and frustration for me. As a stranger living for many years in foreign countries, I have had to constantly negotiate the meaning of rules and practices that more often than not I did not fully understand, the subtleties of a social language that was not my mother tongue. Norms are the language a society speaks, the embodiment of its values and collective desires, the secure guide in the uncertain lands we all traverse, the common practices that hold human groups together. The norms I am talking about are not written and codified; you cannot find them in books or be explicitly told about them at the outset of your immersion in a foreign culture. We learn such rules and practices by observing others and solidify our grasp through a long process of trial and error. I call social norms the grammar of society because, like a collection of linguistic rules that are implicit in a language and define it, social norms are implicit in the operations of a society and make it what it is. Like a grammar, a system of norms specifies what is acceptable and what is not in a social group. And analogously to a grammar, a system of norms is not the product of human design and planning.