Method acting, known as the Method, is a group of rehearsal techniques that seek to encourage sincere and expressive performances through identifying with, understanding, and experiencing a character's inner motivation and emotions. Theatre practitioners built these techniques on Stanislavski's system, developed by the Russian and Soviet actor and director Konstantin Stanislavski and captured in his books An Actor Prepares, Building a Character, and Creating a Role.

The approach was initially developed by three teachers who worked together at the Group Theatre in New York and later at the Actors Studio: Lee Strasberg, who emphasized the psychological aspects; Stella Adler, the sociological aspects; and Sanford Meisner, the behavioral aspects.

"The Method" is an elaboration of the "system" of acting developed by the Russian theatre practitioner Konstantin Stanislavski (1863–1938). In the first three decades of the 20th century, Stanislavski organized his training, preparation, and rehearsal techniques into a coherent methodology. The "method" brought together and built on the director-centred unified aesthetic and disciplined ensemble approach of the Meiningen company; the actor-centred realism of the Maly Theatre; and the naturalistic staging of André Antoine and the independent theatre movement.

The "system" cultivates what Stanislavski calls the "art of experiencing", to which he contrasts the "art of representation". It mobilizes the actor's conscious thought and will to activate other, less-controllable psychological processes, such as emotional experience and subconscious behavior, sympathetically and indirectly. In rehearsal, the actor searches for inner motives to justify action and the definition of what the character seeks to achieve at any given moment (a "task").

Stanislavski later elaborated the "system" with a more physically grounded rehearsal process, the "Method of Physical Action". Minimizing at-the-table discussions, he began to encourage an "active analysis", in which the sequence of dramatic situations are improvised. "The best analysis of a play", Stanislavski argued, "is to take action in the given circumstances."

Another important influence on the Method were the ideas and techniques of Yevgeny Vakhtongav, a Russian-Armenian student who died in 1922, aged 39. Vakhtangov's "object exercises" were developed by Uta Hagen to train actors and maintain their skills. Strasberg attributed to Vakhtangov the distinction between Stanislavski's process of "justifying" behavior with the inner motivational forces that prompt that behavior in the character and the "motivating" behavior with imagined or recalled experiences relating to the actor and substituted for those relating to the character. Following this distinction, actors ask themselves, "What would motivate me, the actor, to behave in the way the character does?" The contrast is the Stanislavskian question, "Given the particular circumstances of the play, how would I behave, what would I do, how would I feel, how would I react?"

In the United States, the transmission of the earliest phase of Stanislavski's work via the students of the First Studio of the Moscow Art Theatre (MAT) revolutionized acting in the West. When the MAT toured the US in the early 1920s, Richard Boleslawski, one of Stanislavski's students from the First Studio, presented a series of lectures on the "system" that were eventually published as Acting: The First Six Lessons (1933). The interest generated led to a decision by Boleslawski and Maria Ouspenskaya (another student at the First Studio who later became an acting teacher) to emigrate to the US and to establish the American Laboratory Theatre.

However, the version of Stanislavski's practice these students took to the US with them was that developed in the 1910s, rather than the more fully elaborated version of the "system" detailed in Stanislavski's acting manuals from the 1930s, An Actor's Work and An Actor's Work on a Role. The first half of An Actor's Work, which treated the psychological elements of training, was published in a heavily abridged and misleadingly translated version in the US as An Actor Prepares in 1936. English-language readers often confused the first volume on psychological processes with the "system" as a whole. Many of the American practitioners who came to be identified with the Method were taught by Boleslawski and Ouspenskaya at the American Laboratory Theatre. The approaches to acting subsequently developed by their students—including Lee Strasberg, Stella Adler, and Sanford Meisner—are often confused with Stanislavski's "system".