In analogy to the private equity market, a new market segment has emerged in the context of stricter lending practices by banks: private debt. Informal private debt, which refers to the direct sale of non-listed bonds and profit-sharing certificates to a wide range of private investors, demonstrates its innovative character by largely dispensing with banks in their intermediary role for small and medium-sized enterprises. Rainer Bizenberger conducts a comprehensive investigation into the forms of informal private debt, the structure and functionality of this market segment, the execution of such transactions, as well as the suitability and design of informal private debt from the perspective of innovative corporate finance. In addition to providing the first market overview of this segment of the gray capital market, he also highlights its key features.