The quartos are the earliest editions of Shakespeare, published in his lifetime or just after. They are physically small and thin. In this time period, plays were not considered serious literature, so they were not printed in large, imposing sizes. These books were intended to be used--and the worn natures of the Haverford copies attest to that.
These quarto editions are of plays that have some controversy over whether Shakespeare wrote all or part of them.
The publishers and printers defied convention when they issued Shakespeare's collected works in a large folio volume (twice the size of a quarto, and often reserved for reference works or collections of famous authors) in 1623. This and the three other folio editions of Shakespeare published in the century after his death are known as the Folios.
These books discuss the history of the printing of the folios and quartos of Shakespeare, and also provide an insight into the collectors who treasured these items over the past four centuries.