In Greg's first major work, A List of English Plays Written before 1643 and Printed before 1700 (1900) but particularly in the "Essay Introductory" printed in A List of Masques, Pageants,&c. Supplementary to A List of English Plays (1902), he laid the foundations of his monumental A Bibliography of the English Printed Drama to the Restoration (London: Bibliographical Society, 1939–1959 in 4 volumes). Frequently scorning the bibliographical status of checklists prepared for literary purposes but denying that it was the task of bibliographers to make descriptive bibliographies (of the systematic kind), Greg described his own Bibliography to be merely descriptive. In papers throughout his career he defined bibliography as "the science of the material transmission of literary texts", defined the scope of bibliographical investigation, and established the essence of bibliographical method as 'critical'—now termed 'descriptive' bibliography—and textual criticism and critical bibliography are synonymous. The Bibliography is widely regarded as a monument of descriptive bibliography.