Frances Luttikhuizen's book is not only an interesting work which claims to analyse an unknown part of the history of Protestantism, but is also a valuable contribution to our understanding of a complex and troubled period in early modern history; the book's main goal is to study the arrival, reception and suppression of Protestantism in sixteenth-century Spain. In particular, and beyond interpretations that focus on the actions of the Spanish Inquisition, the Protestant Reformation had a significant impact in the Iberian Peninsula during the sixteenth century, largely owing to the activity of several groups of intellectuals, religious movements and public figures. In the first part of the book (chapters i–iv), the author aims to offer an overview of the origins of Protestant ideas or, in the author's own words ‘underground Protestantism’, in Spain. During the closing decades of the fifteenth century and the beginning of the sixteenth, the cultural climate in Spain was open to the reception of new ideas. For instance, Cardinal Cisneros and the University of Alcalá were key elements for the dissemination of Erasmus’ ideas and, at the same time, several emerging movements promoted the development of new forms of spirituality through a mystical return to God. One of the most relevant of these movements was that of the alumbrados-deixados, which is analysed in depth by Luttikhuizen. Chiefly, this movement advocated an intimate approach to Christianity. Other important personalities, such as Juan de Valdés, shared the deixados’ longing for new forms of religiosity. The second part of the book (chapters v–x) focuses on Protestantism itself, i.e. Protestant episodes in the Iberian Peninsula. During the difficult reign of Charles v (1516–56), some revolts and popular movements were directly related to Luther's proposals, and the arrival of clandestine Protestant literature played a significant role. This is the origin of the ‘Index of Prohibited Books’. In these chapters, Luttikhuizen analyses, on one hand, the emergence of Protestant circles in Valladolid and Seville, and, on the other hand, the work of a number of important writers, including women. Finally, the third part of the book (chapters xi–xiii), focuses on exile and repression. Of special interest is Luttikhuizen's description of the lives of Spanish Protestant exiles such as Enzinas, Alejandro, Castillo, De la Cruz, Zapata and Pérez de Pineda and her account of the climax (but nor the end) of anti-Lutheran repression, with the celebration of several autos de fe in 1559–60. During the second half of the sixteenth century, the Inquisition increased the social and cultural pressure on Lutheran sympathisers, and numerous exemplary sentences were passed. In conclusion, Luttikhuizen's work is a very interesting contribution and a suggestive and valuable work for our understanding of a traditionally neglected part of the history of the Reformation. Although Spain was the birthplace of the Counter-Reformation, Protestantism was substantially present in the Iberian Peninsula, and the significant implications of this for the overall history of the Reformation need to be taken into consideration.