Ephesians 6:11 calls upon readers to, ‘[p]ut you on the armor of God, that you may be able to stand against the deceits of the devil.’ This dissertation puts this verse at the center of devotional practice in thirteenth- to fifteenth-century England by showing that books and stories were often perceived as that very armor. Just as St Boniface reportedly held up a scriptural manuscript at his moment of martyrdom to protect himself from the sword, medieval readers saw their books, and the texts contained within them, as spiritual and physical protection against devilish attacks. Not only were texts adapted and manipulated by redactors for defensive reading, the form of the manuscripts themselves encouraged their readers to treat them as allegorical, even literal, shields. In order to evidence this reading practice, this dissertation explores the transmission history, textual content, and cultural contexts of two Middle English verse texts. Part I shows how ‘O Vernicle,’ a fourteenth century lyric on the arma Christi (the ‘arms of Christ’), exemplifies the ritualistic nature of defensive reading. Extant in ten rolls and ten codices, the textual presentation encourages the reader to imaginatively arm themselves with the arma Christi, turning those weapons once used against Christ into their ‘armor of God’ (Eph. 6:11). Part II focuses on the late thirteenth-century collection of sanctorale and temporale entries known as the South English Legendary. It deals predominantly with an early reader of the collection – a redactor whose ‘edits’ transformed the historical trajectory of the South English Legendary, imbued it with a defensive purpose, and shaped the way it was recopied through the fourteenth and fifteenth century. The content of both texts, made up of image/text arma Christi units and hagiographic vitae and temporale respectively, divide and compartmentalize the reading experience. This suits the defensive agenda, allowing the reader to collect ‘textual shields’ as spiritual armor. Putting on the Armor of God defines a widespread cultural practice – ‘defensive reading.’ It demonstrates not only that medieval readers consciously read certain devotional Middle English texts in order to defend themselves against spiritual evils, but also that they were copied and redacted with this purpose in mind. Ultimately it shows that, in the later Middle Ages, reading was a way of putting on the ‘armor of God’ (Eph. 6:11).