[영문]I study the security design problem of a firm when investors rather than managers have private information about the firm. I find that it is often optimal to issue information-sensitive securities such as equity. The qqqquot;folklore proposition of debtqqqquot; from traditional signaling models only goes through if the firm can vary the face value of debt with investor demand. When the firm has several assets, debt backed by a pool of assets is optimal when the degree of competition among investors is low, while equity backed by individual assets is optimal when competition is high