John Bunyan’s The Pilgrim’s Progress, first published in 1678, has played an important role in Christian mission work and is remembered as one of the first modern novels. In 1830 the book was entitled the ‘English Literature Cannon,’ and has been translated into many languages, second only to the Bible. This honor and popularity is due mainly to Bunyan's fine writing style and fertile literary imagination; however, the illustrations added to each version and print - that is, the visualizations of the content - were crucial to maintaining popular interest in and understanding of the book. Illustrations can have a major influence on the reputation and authority of a book. However, researches on book illustrations are rarely found in Korean scholarly works. As a foundational research, therefore, this article explores the illustrations of various prints of The Pilgrim’s Progress by six artists and role and development of the illustrations, consulting works of Gerda S. Norvig on the subject. Illustrations first appeared in the fourth edition of the book in 1680, two years after the first edition. Although the book had only two drawings, the event became the critical moment for the gradual emergence of book illustrations which also influenced and changed the constitution of the book itself. Of the illustrations in the book’s early days, it was the fourteen drawings in the fifth edition (1682) that first covered and visualized the general content of the book. But because adding book illustrations was a new development, the illustrations were far from eloquent and skillful in their design and carving technique. Three years later, a Flemish-French translation of the book appeared with nine illustrations by a Dutch poet and engraver Jan Luiken. These illustrations, engraved out of copper plates, show an advancement in the expression and technology of craftsmanship. In the eighteenth century, John Sturt’s fourteen illustrations were included in the 22nd edition, so-called the Queen Caroline edition (1728). The illustrations are praised for their unique aesthetical elements while maintaining the tradition of former editions. In 1788 eight drawings by Thomas Stothard were issued separately from the 1788 edition. Compared with the craftwork on the former illustrations, the painter prettified the design, which still remained in the tradition of genre-painting. Stothard's illustrations became popular, deeply influencing illustrations in the coming ages. In the nineteenth century, the number of illustrations in The Pilgrim’s Progress increased while qualitative changes also appeared. In 1824 painter William Blake produced 28 mysterious watercolor illustrations based on his meditation and imagination. Henry Courtney Selous' 58 illustrations were placed in the 1844 Rev. Maguire annotated edition. Despite the busy composition, his works are acclaimed as expressing the theme of the book in distinct and dynamic ways. Throughout the three centuries of the book’s history, it was the famous artists of the age that improved the quality and creativity of the illustrations of The Pilgrim’s Progress. The illustrations in the book had been drawing the attention of readers to the text and leading them to understand briefly the pilgrimage to the Celestial City, regardless of readers’ literacy. Particularly in the nineteenth century, the illustrations themselves were recognized and developed as an independent field, not as a part of the book. The drawings now spoke for themselves apart from the text, and people could comprehend the whole story only by appreciating the images. Surely, the story of the book in visualized illustrations imprinted smoothly in the reader’s memories. This article also briefly deals with the American illustrations of The Pilgrim's Progress.