Martín de Azpilcueta (Azpilkueta in Basque)[1] (13 December 1492 – 1 June 1586), or Doctor Navarrus, was a Navarrese canonist, theologian and economist.

Congitating about the effects of gold and silver arrivals from the Spanish Empire, Azpilcueta independently formulated the quantity theory of money in 1556.

His Manual de confesores y penitentes (1549), originally written in Spanish, was enormously influential in the fields of canon law and ethics, and by the first quarter of the seventeenth century, it had gone through 81 editions.

[14] He formulated a basic form of the principle of contractual consensualim, which was later elaborated upon by other members of the School of Salamanca like Leonardus Lessius and Pedro de Oñate [fr].

[15] Azpilcueta cogitated also on the concepts of commutative justice, just price and fairness in exchange: with a large interpretation of the principe of laesio and of the seventh Commandment, he considered that contracts doesn't be burdens for a party and that any violation of the equity can be take to ecclesiastical courts.

[17] Later, he had to explain in his 1586 Miscellaneum centum that vernaculars had been used before, as approved by bishops and inquisitors, citing "a pious and knowledgeable Cantabrian", referring to Sancho de Elso from Estella, who had used Basque in different prayers.