「幕表戲」是「即興戲劇」的一種，臺灣歌仔戲藝人稱「演幕表戲」為「做活戲」。憑「幕表」（「臺數」）編劇是歌仔戲職業劇團的看家本領，無論在「內臺」或「外臺」時代，它一直都是民間編劇的主要創作方法。 它先由「講戲人」編出一個情節骨幹，再交由演員上臺臨場發揮，將戲肉填滿。這原是順應過去藝人多半未受教育，偏偏劇目需求量又很大的客觀環境所發展出來的編劇技術。然而，在今天教育已然普及，外臺歌仔戲的中生代藝人編劇，仍然沿續這樣的方式作為他們最主要的編劇手段，說明了此一創作方法的有效和不可取代。 本文以臺灣歌仔戲為對象，透過文獻分析、田野觀察和訪問，首先概論通俗即興劇場的特質，以及歌仔戲長期活動於通俗即興劇場所形成的戲劇觀。在此基礎上，探索歌仔戲「幕表」編劇的創作機制，並試圖掌握其創作的具體法則。

Improvisational in nature, the “scenario drama” is what performers of Taiwanese Opera call “doing live shows.” To compose a drama based on sketchy scenarios is how the professional troupes showcase their talents. Whether during the “indoor theatre” or “outdoor theatre” period, it has always been a major mode in which the dramas of Taiwanese Opera are created. It starts with a basic plot outline provided by the “scenario teller” and is finally completed in a full-fledged dramatic form collaborated by performers on stage. This mode of playwriting was derived from the fact that most performers in the past were illiterate and also that there was a great demand of materials. Though illiteracy is no longer a problem, however, dramas of the “outdoor period” today are still composed in this fashion. This illustrates the effectiveness and indispensable quality of the “scenario drama.” The present study, through careful examination of documents and extensive field research as well as interviews, first explores the improvisational nature of Taiwanese Opera, and, more important, its general dramatic outlook as colored by this quality of impromptu. Then the discussion will move on to investigation the creative mechanism and specifics methods of the “scenario drama.”