ENFrom childhood, the son of Sigismund the Old and Catherine Telniczanka, John of the Lithuanian Dukes (1499-1538), knew he was a prince, and so did his contemporaries. However, maintaining a princely estate does not come cheaply. The aim of this article is not to examine in detail the financial records of this princely cleric, for such documents no longer exist, nor shall we speak in general of the official income of the bishops of Vilnius; rather, we shall examine, where the meagre sources permit, how the bishop garnered income from property deals, the patronage of artisans, loans, and tax farming to fund his activities as a prince of the Church and a responsible secular lord. A broad account is given of John’s income and expenditure in childhood, his clerical career in the sees of Płock, Poznań and Vilnius, and his acquisition of property in Šiauliai and Volyn. Attention is also paid to the bishop’s use of the adoption law to his financial advantage. John was by no means a poor man but he was not as wealthy as he might appear – he promised to pay for building work in Poznań but left debts; he was expected to restore the city walls, but died prematurely. He pledged to present the Poznań cathedral treasury with a golden chalice but left only a debt of 300 złoty; the same goes for the ring he promised on his joyful ingress into his new see. He was economically astute – he built the first glass foundry in Vilnius on condition it provide him with window glass and tableware.He purchased houses and rented them out for long term occupation – the rent of at least three generations of Kirchel burghers in Vilnius funded his mansionary chapel in Vilnius cathedral. He gives the impression of never having enough ready cash at hand, despite obtaining large swathes of financially profitable grand-ducal territory which produced the considerable income he needed to spend on administration. Keywords: John of the Lithuanian Dukes; Vilnius bishop; income; debts; status. [From the publication]