Transubstantiation

Catholic belief that bread and wine turn into Christ's flesh and blood in the sacrament of the eucharist. Protestant creeds thought this part of the Catholic idolatry, superstition and "hocus pocus". In the Thirty-Nine Articles transubstantion was expressly considered as non-scriptural:

"XXVIII. Of the Lord's Supper. The Supper of the Lord is not only a sign of the love that Christians ought to have among themselves one to another, but rather it is a Sacrament of our Redemption by Christ's death: insomuch that to such as rightly, worthily, and with faith, receive the same, the Bread which we break is a partaking of the Body of Christ; and likewise the Cup of Blessing is a partaking of the Blood of Christ.

Transubstantiation (or the change of the substance of Bread and Wine) in the Supper of the Lord, cannot be proved by Holy Writ; but is repugnant to the plain words of Scripture, overthroweth the nature of a Sacrament, and hath given occasion to many superstitions.

The Body of Christ is given, taken, and eaten, in the Supper, only after an heavenly and spiritual manner. And the mean whereby the Body of Christ is received and eaten in the Supper, is Faith.

The Sacrament of the Lord's Supper was not by Christ's ordinance reserved, carried about, lifted up, or worshipped" (http://anglicansonline.org/basics/thirty-nine_articles.html)

In the 17th century, the Test Acts made people who wanted to take public office swear that they did not believe in transubstantiation.

Source:

Anglicans Online: http://anglicansonline.org/basics/thirty-nine_articles.html.