Because of how intertwined they eventually became, I've consolidated the Dramabooks lines to one page. Thus the page includes information for the Dramabooks proper, Mermaid Dramabooks, New Mermaids, Spotlight Dramabooks, and the merged lines of the 1970s and 1980s.
The Dramabooks and Mermaid Dramabooks were both launched by Hill & Wang in 1956 in a pocket paperback format. The Dramabooks proper were books about the theater, whether criticism, scholarship, or biography. The Mermaid name was taken from the earlier Mermaid Series of English Dramatists line, which Hill & Wang acquired when it took over the A.A. Wyn back catalog upon formation in 1956. These Wyn backlist titles were released as Mermaid Dramabooks, a series which also included new collections of plays by well-known playwrights.
The Spotlight Dramabooks series was begun in 1960 and focused on single contemporary plays until 1972, after which the Spotlight line seemingly and effectively became the Mermaid Dramabooks line, which from then until 1988 published single plays by contemporary authors. The New Mermaids were launched in 1966 and focused entirely on works from the Elizabethan and Jacobean theatre.
In terms of series numbers, each line started out with its own prefix and succession of numbers. D- indicated Dramabooks, MD- the Mermaid Dramabooks and New Mermaids, and SD- the Spotlight Dramabooks. With the adoption of SBNs/ISBNs by Hill & Wang around 1968/1969, the prefixes were dropped and the series numbers continued as part of the book number (e.g., the Dramabooks line went from D45 in 1968 to 0546 in 1969, a number that was reflected in its book number: 0-8090-0545-8).
Between 1969 and 1972, each line had its own separate numbering system: the Dramabooks used 05xx, the Mermaid Dramabooks used 07xx, and the Spotlight Dramabooks used 12xx. With the end of the Spotlight line in 1972, the Dramabooks all* moved to the 12xx numbers, continuing from where the Spotlight line, 1217-1227, left off and running from 1228-1253 (1972-1988). All of these titles were single plays by contemporary playwrights, thus continuing the Spotlight concept, albeit not under that name. Curiously, the first two of these new titles, 1228 & 1229, were published as Dramabooks in 1972, but all others from 1230-1253 (1973-1988) were published under the Mermaid Dramabooks line. Perhaps Hill & Wang decided Mermaid had a more distinctive flair.
* With the exception of two Dramabooks proper, 0550 (1977) and 0551 (1985).
At any rate, here's all that broken down by line:
Dramabooks: works on drama from 1956-1972, 1977, 1985; two contemporary plays in 1972
Mermaid Dramabooks: collections of plays from 1956-1973; single contemporary plays from 1972-1988
New Mermaids: Elizabethan and Jacobean plays
Spotlight Dramabooks: single contemporary plays
Hill & Wang (H & W) earned its initial reputation by inaugurating the Dramabooks series (1952). Dramabooks originally presented the work of such drama critics as G. K. Chesterton and George Bernard Shaw. Its Mermaids series also presented seventeenth-century English plays. Eventually, the works of such twentieth-century playwrights as Jean Cocteau, Jean Giraudoux, Jean Anouilh, Max Frisch and Arthur Kopit were added to the Dramabooks series. Dramabooks also includes ten volumes of Lanford Wilson's plays including Hot L Baltimore (1970).
From inside MD3:
Hill and Wang aims to establish DRAMABOOKS as a permanent library of the great classics of the theater of all countries, in an attractive, low-priced format.
From the back cover of The Alchemist, MD 105:
The New Mermaids are scholarly, low-priced editions of Elizabethan, Jacobean, and Restoration Plays. Each New Mermaid is published in a separate volume, in both cloth and paper, and is edited by an outstanding authority who contributes an introduction in which dates, authorship, sources, textual problems, and criticism are brought under review. The texts have been carefully re-established from early printed editions and comprehend the most recent findings of modern research. Critical notes, textual variants, and reading lists are also provided. Published volumes are listed below.
Hill & Wang to Issue Drama Paperbacks in August, PW, May 21, 1956, at 2130.
Hill & Wang to Publish Second Dramabook Series, PW, May 16, 1960, at 44-45 (announcing the Spotlight Dramabooks, each of which focuses on a single play by a leading American or foreign playwright and is published in a larger 5 3/8 x 8 inches format).
The New Mermaids . . ., PW, Jan. 31, 1966, at 89 (announcing the New Mermaids in conjunction with the 10th anniversary of Hill & Wang as a series focused on great works of the Elizabethan and Jacobean stage, general editors Philip Brockbank and Brian Morris, both of the University of York).