Shakespeare's first play was most likely Henry VI Part I, which was first performed between 1590 and 1591 and printed in 1594. Because no recorded dates exist for first performances of any of Shakespeare's plays, scholars have to make decisions based on several types of information.
References to actual events of the time, personal diaries of actors and other contemporaries, print dates and royal court records are sources used in constructing time-lines of performance. Playwrights in the Elizabethan age had to register their work. It was subject to heavy censorship, so many of them wrote under assumed names or avoided registering. Additionally, Shakespeare never claimed authorship of any of his work nor did he oversee printing. These factors combined make nearly impossible to accurately date performances.