Book excerpt: Entrepreneurship scholars have resolved that overconfidence may play a role in entrepreneurial decisions. Although informative, extant research offers limited explanations on the mechanisms through which overconfidence contributes to the observed behavior. Moreover, important aspects of uncertainty and ambiguity, quintessential in entrepreneurial activity, are nearly neglected, and most studies focus on risk. My dissertation investigates entrepreneurs' attitudes towards ambiguity and the impact of overconfidence. Given this goal, I employ modern ambiguity theories and design several experiments, each aimed at responding to a precise research question, contributing to the grand theme of the manuscript. Findings suggest that overconfidence enhances decision makers' proneness to ambiguity, and both phenomena are context-related and likelihood dependent. I also find that entrepreneurs are more optimistic than non- entrepreneurs when deciding both under risk and ambiguity. Yet, entrepreneurs are more pessimistic under ambiguity compared to risk, while non-entrepreneurs do not discriminate between the two. The contribution of my work consists in bringing entrepreneurs where they belong: deciding under ambiguity... in the laboratory or in the wild.