Three great acting parts, strong dramatic incidents and plenty of opportunities for scenery and costume are enough to explain the steady success of King John with both stage and audience. Shakespeare's handling of the relations between the English King and the Pope leaves the play unfit, as it stands, for use in propaganda on either side; and the invasion of England by the French has not been caught at in times of similar danger so much as might have been expected. The importance of the play in theatrical history lies in its being the chief vehicle for the introduction of archaeology into the theatre.

In his Introduction and elsewhere in this volume Professor Dover Wilson gives his reasons for thinking that Shakespeare's King John in its earliest form may have been first performed by some company unknown in 1591—that is, as much as five years before the death of his son Hamnet in August 1596 could have ‘taught him what true grief was.’ Before the mention by Meres in 1598 there is no external evidence to fix the date. Its name is in the list, dated January 12, 1669, of ‘part of his Mates Servants Playes as they were formerly acted at the Blackfryers and now allowed of to his Mates Servants at the New Theatre’; but there is no evidence that the King's Company ever performed it.