The purpose of this paper is to analyze the relevance of foreign law in a specific work of the Portuguese jurist Manuel Álvares Pegas (1635-1696), the Allegaçam de direito por parte do excelentíssimo senhor Dom Pedro de Menezes sobre a sucessão do título, e estado de Villa-Real, e Morgados da dita Caza e bens patrimoniais que a ella pertenencem, e ao dito Senhor sucessor de ella. The paper firt address two issues: general features of the allegationes as a genre of juridical literature and the concept of foreign law in the Early Modern Age. The study further concerns the use of foreign law in this particular work and the meaning of this application.