This is too broad a question! Here are just a few in a nutshell
1. Realism--realistic or representational theories of theatrical communication. From Ibsen to Shaw, one can draw a line here in this ideological, socially committed and ideational theatre of realistic representation. You can read Shaw's Quintessence of Ibsenism.
2. Expressionism--the focus is on expression through a symbolic medium. Strindberg's plays are a case in point.
3. Absurdism--the anti-realistic theatre that shifts the focus from sense to nonsense, critiquing the production of meaning in theatre. Ionseco and Beckett, even Pinter are the examples.
4. Actor-training--from Stanislavskian realistic acting of 'psycho-technique' to Stratsburg's 'method' acting to Grotowski's 'holy acting' in the 'poor theatre' (abandonning scenary, stage, props and so on) to Artaud's phenomenolgical 'theatre of cruelty' (a kind of theatre of the senses)
5. A-Effect and Brecht--'gestic' (a gisting gest to sum up performance) acting as a critique of realism, laying bare the medium through alienation effect in acting that breaks open the illusion of reality in the representational theatre.
6. Performance theory--from Herbert Blau to Richard Schechner--the focus on performance as opposed to the play-texts, study of performance history and techniques, adaptations and so on.
Have a look at Eric Bentley 's book on 'The Theories of Modern Stage'
Some of the important developments in modern drama are expressionism, epic theatre, symbolism, surrealism, and the theater of the absurd.
1. Expressionism: Expressionism in drama was concentrated in Germany in the early 20th century. Friedrich Carl Georg Kaiser (1878-1945) was the most famous expressionist dramatist. His popular plays include "From Morn to Midnight" and "The Burghers of Calais." The main feature of expressionism is a distortion of physical reality to highlight certain emotional effects and convey personal moods and feelings.
2. Epic Theater: The chief proponent and successful practitioner of this form of modern drama was the German dramatist Bertolt Brecht (1898-1956). Its main feature was the use of the ancient epic convention of choruses and projections as a means of commentary. "Mother Courage"(1939) is Brecht's most famous play.
3.Symbolism: The aim of symbolism was to capture absolute truth by indirect methods. Symbolism emphasized mysticism, and the life of dreams and fantasies. The most famous symbolist theater person was Maurice Polydore Marie Bernard, Count Maeterlinck (1862-1949). His most famous play is "The Blue Bird" (1908).
4. Surrealism: Wilhelm Albert Włodzimierz Apolinary Kostrowicki, (1880-1918) is the foremost surrealist playwright and his most successful play is 'The Breasts of Tiresias' (1903,1917). Surrealism's main is to reveal the dynamics of the sub conscious and is characterized by fantastic imagery and juxtaposition of bizarre subject matter.
5. Theater of the Absurd: As the word 'absurd' indicates the dramas of the "Absurd" reveal the meaninglessness of modern life and depict man as a puppet controlled by some bizarre external force. Some of the important playwrights of this type of drama are Samuel Beckett and Harold Pinter. Beckett's "Waiting for Godot" (1948,1953) is one of most important plays of the twentieth century.
Please read the book "Modern Drama:Critical Concepts" edited by Martin Puchner.
Social and Psycho Drama
According to advance Oxford learners dictionary f English, Psycho drama is "a play of film/movie that makes the minds and feelings the character more important than the event". This is a play or drama with a therapeutic effect on the people wo either psychologically or mentally are inbalanced. "pshychlogy is scientific study of how the mind influences behaviour in a particular area of life" Sam Iyanda (2004:45) his is scientific study of behaviour.
Psycho drama encourages immaginative developmens to cteate pictures of ideas, thoughts and technological development in mind. Even representational acting (realistics) also rely on immagination in character creation to review the "inner truth" the man with the greatest influence in acting and Father of modern actor training in his theory of acting encourage this.
Social drama is one that interact with the audience bringing a feed back as a result of effective communication. this drama is socially commited to the exploration of human conditions such as wickedness, hatred, oppression, civiliazation etc. and why solution have failed and offers its own solution.
Oxford Advanced Leaners Dictonary of English 7th ED
Topics in Drama and Theater by Samuel Iyanda etal 2004.
THA 209 & THA 207 Lecture NOTE Benue State University Makurdi Nigeria
they are symbolism and surrealism.