The traditional capital structure problem usually includes the firm choice between debt and equity. In the last 20–30 years a security design line of research has emerged that considers a more general question, i.e., why even debt and equity exist as the only possible financing choice; are there any ways to explain and model the firm’s choice of possible securities on a more abstract level. Chapter 11 deals with these questions. It will also demonstrate that such a more general approach creates good practical value for the capital structure area, e.g., it helps to identify and create new types of securities. The chapter also focuses on some latest innovations in the area of financing including hybrid securities, PIPE, SPAC, and VIE.