St Bridget of Sweden (1303-73) began to experience supernatural revelations as a lady-in-waiting at the Swedish court in 1335. After her husband's death she left the court and founded a monastery for nuns and monks which became the basis of the Brigettine Order. Her visions continued after she left Sweden for Italy in 1349, and she spent the rest of her life in pilgrimage and religious activities. The visions, some of the Passion and others concerned with political and religious events of her day, were recorded in Latin by her spiritual directors, as the Liber Celestis. The mystical equivalent of a medieval manual for preachers, the work points us to what was best and worst in late medieval spirituality. It was several times translated into Middle English but the only translation hitherto available has been the partial and truncated version published in 1929. The present work is a critical edition of one of the two complete Middle English translations of the Liber, contained in British Library MS Claudius BI. This first volume consists of the text and a brief introduction to the Liber. The second volume will include a study of the manuscript and the translation; a full commentary, explanatory notes, bibliography, and glossary.