Abstract: Decision makers do not make choices in a vacuum. They make them in an environment where many features, noticed and unnoticed, can influence their decisions. The person who creates that environment is, in our terminology, a choice architect. In this paper we analyze some of the tools that are available to choice architects. Our goal is to show how choice architecture can be used to help nudge people to make better choices (as judged by themselves) without forcing certain outcomes upon anyone, a philosophy we call libertarian paternalism. The tools we highlight are: defaults, expecting error, understanding mappings, giving feedback, structuring complex choices, and creating incentives.