This paper analyzes the impact of entrepreneurial optimism on the market for new issues. We find that the existence of optimists generates a new reason for entrepreneursto own equity in their firms. We show that optimism is a natural explanation for why some new issues are underpriced and others overpriced. We also show that the impact of optimism on entrepreneurs' equity holdings depends on the number of optimists, absolute risk aversion, and cash flow variance. Optimism makes entrepreneurs worse off. In contrast, optimism can make outside investors better off when entrepreneurs signal firm value by retaining shares and underpricing.