In German corporate law, there is fundamentally freedom of financing. Shareholders can decide whether to provide additional equity or debt capital alongside the statutory minimum equity of the company. There is still no obligation for shareholders to equip a company with equity in a risk-appropriate manner. The law on equity substitution establishes a responsibility for the financing consequences of shareholders, who provide shareholder contributions as debt capital to the company at a time when the shareholders, as ordinary merchants, would have contributed equity (during the company's crisis). The shareholder financing granted or left in place during the crisis is treated as an equity-substituting contribution if certain further conditions are met. The issue of equity-substituting shareholder contributions primarily arises in the event of the company's insolvency. The study aims to highlight the key issues of capital substitution law in the context of insolvency proceedings and to delineate the relevant scope of application through a presentation of classical and modern case groups.