Willem Hessels van Est, Latinized as Estius (1542 – 20 September 1613), was a Dutch Catholic commentator on the Pauline epistles.

During this time he was frequently the bearer of pecuniary aid to his uncle, Nicolas Pieck, who was giving missions in present Belgium; but the latter would never accept any help.

The father and brother escaped, but Nicolas Pieck, who was then Superior of the Franciscan convent at Gorcum, and eighteen other ecclesiastics, were taken to Den Briel, on the North sea-coast, and put to death.

When Est first arrived at Leuven he found the place in a ferment owing to the recently broached opinions of Michel Baius, one of the professors of Holy Scripture, who held a leading position in the university all the time that Est was there; violent controversy raged around the person of Baius during all that time.

It is evident from the commentaries of Est that he was much influenced on questions of divine grace and free will by the teaching of his old professor, Baius; and on these points he has to be read with some caution.

The friends of Baius, who admired him for his edifying life, great learning and manly submission, felt annoyed that his shortcomings should have been thus pointedly accentuated by their opponents.