An ancient English diocese, it was established with the authority of King Æthelberht of Kent by St. Augustine of Canterbury in 604, at the same time as the see of London; only the adjacent diocese of Canterbury is older than that of Rochester in England. Its establishment was the first part of an unrealised plan conceived by Pope Gregory the Great that Archbishop Augustine should consecrate twelve bishops in different places, and then twelve more under the prospective See (later Province) of York.
The diocese is subdivided into three archdeaconries:
The current diocesan boundaries roughly match its pre-19th century extent. On 1 January 1846 parishes in Hertfordshire from the dioceses of Lincoln and of London and Essex (from London Diocese) were added to Rochester, while all West Kent parishes except those in Rochester Deanery were transferred to the diocese of Canterbury. In May 1877 Essex and Hertfordshire became part of the newly-created diocese of St Albans. Subsequently, on 1 August 1877, Rochester Diocese gained northern parts of Surrey in the diocese of Winchester, which later were transferred to the diocese of Southwark upon its creation in 1905.