This dissertation studies the history of two generations of a transnational business family (1779–1866). Originally from the Basque Country, the Tastets became prominent global trade actors in the late eighteenth century. Their diversified portfolio of business activities included, mainly, shipping, insurance and banking. The relevance of the two main business branches, namely Antonio de Tastet & Cía. of San Sebastian (Spain), and Fermin de Tastet & Co. of London (England), contrasts with the limited number of documents they have left in small archival collections. Without a centralized archive from which to draw accounts, balances and correspondence, proceeding to a classic study of the firm’s history does not look initially very promising. Taking a detour from conventional sources, I instead follow the traces of the family and their companies in a different space: courts. Commercial transactions were complicated during the Napoleonic Wars (1804–1815), and judges found it difficult to assess the truth in the evidence that litigants displayed. Their solution was to examine the parties’ credit and use it as a proxy for truth. This turned credit into capital and triggered Fermin de Tastet’s process of litigatory capital accumulation. Drawing mainly from the numerous bills and answers filed by and against Fermin de Tastet in the Chancery Court (England), this dissertation shows that litigation records are an extremely productive source to use to write the history of a company or a business family and to write business history more generally. It also shows how certain institutions for capital allocation, including (surprisingly) forensic psychiatry, played a fundamental role in the life of the Tastets and other business families.