Alonso de Idiáquez y Yurramendi (1497–1547), known in Basque as Alfontso Idiakez, was a Spanish nobleman and politician. He was born in Tolosa, Gipuzkoa.

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Idiáquez began his career working for Francisco de los Cobos, and became royal secretary to Charles I of Spain. He was a knight of the orders of Alcántara, Calatrava and Santiago.^[1]

Idiáquez was the dedicatee of a book on letter-writing, De conscribendis epistolis published in the 1530s. He met the author, Juan Luis Vives, in the Habsburg Netherlands.^[1] Vives begins by telling “Señor Idiáquez” to always consider the rhetorical situation for the letter, primarily evaluating the relationship of the writer to the recipient.

He may have commissioned the illuminated manuscript known as the Munich-Montserrat Book of Hours, which was the work of the Flemish miniaturist Simon Bening. The manuscript is known to have been in the possession of a Dominican friary in San Sebastian associated with Idiaquez.

He met a violent death in Torgau, Germany, at the hands of Protestants. His body was taken back to Spain for burial.

His son Juan de Idiáquez y Olazábal [es] also entered the service of the king.