Under Development
Shakespeare's play possesses a close relationship with an earlier history play, The Troublesome Reign of King John (ca. 1589). The consensus among modern scholars is that the earlier play provided a source and model for Shakespeare's work. However, there is a strong line of oppositional criticism that argues for the priority of Shakespeare's play, beginning with Peter Alexander and continuing with the work of E. A. J. Honigmann. Some critics believe that Shakespeare revised this early version of the play in the mid-1590s. It is possible that The Troublesome Reign is his play or that it is a 'bad quarto' (a memorial reconstruction put together by one or more actors in an earlier stage production).
Other probable sources of note include the Chronicles of Holinshed, John Foxe's 'Acts and Monuments', and Matthew Paris's Historia Maior.