The illuminations of the Chronicle of John of Worcester (c.1140) are among the most famous images of English medieval art and among the earliest images in the history of chronicle illumination. They showcase three frightful dreams suffered by King Henry I of England (interpreted with the aide of the court physician Grimbald) and his subsequent perilous Channel crossing. The images nonetheless remain poorly understood and often misinterpreted. The present study analyzes them closely by considering their relationship to the text, which previous studies have done in only selective ways. In addition to the word-image dynamics, the illuminations are shown here to play a role in the larger work of John’s chronicle, including in relation to its other illuminations. Most importantly, however, the dream images shed light on John’s working practices and his evolving conceptions of history and history-writing. The illuminations are post-factum reworkings of John’s own earlier chronicle entries and the present paper underscores how in the intervening years he gained novel insights into the place of astrology and natural science in his understanding of history. Through his texts and images, John became a dream interpreter in his own right – supplanting Grimbald – and posited his own remarkable views on the meaning of King Henry’s nightmares.