Shakespeare's primary source for Richard II, as for most of his chronicle histories, was Raphael Holinshed's Chronicles; the publication of the second edition in 1587 provides a terminus post quem for the play. Edward Hall's The Union of the Two Illustrious Families of Lancaster and York appears also to have been consulted, and scholars have also supposed Shakespeare familiar with Samuel Daniel's poem on the civil wars.
A somewhat more complicated case is presented by the anonymous play sometimes known as The First Part of Richard II. This play, which exists in one incomplete manuscript copy (at the British Museum) is subtitled Thomas of Woodstock, and it is by this name that scholars since F. S. Boas have usually called it. This play treats the events leading up to the start of Shakespeare's play (though the two texts do not have identical characters). This closeness, along with the anonymity of the manuscript, has led certain scholars to attribute all or part of the play to Shakespeare, though many critics view this play as a secondary influence on Shakespeare, not as his work.