Stanislavski's system is a systematic approach to training actors that the Russian theatre practitioner Konstantin Stanislavski developed in the first half of the twentieth century. His system cultivates what he calls the "art of experiencing" (with which he contrasts the "art of representation"). It mobilises the actor's conscious thought and will in order to activate other, less-controllable psychological processes—such as emotional experience and subconscious behaviour—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").

Later, Stanislavski further elaborated what he called 'the System' with a more physically grounded rehearsal process that came to be known as the "Method of Physical Action". Minimising at-the-table discussions, he now encouraged an "active representative", 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."

Thanks to its promotion and development by acting teachers who were former students and the many translations of Stanislavski's theoretical writings, his system acquired an unprecedented ability to cross cultural boundaries and developed a reach, dominating debates about acting in the West. According to one writer on twentieth-century theatre in London and New York, Stanislavski's ideas have become accepted as common sense so that actors may use them without knowing that they do.

Having worked as an amateur actor and director until the age of 33, in 1898 Stanislavski co-founded with Vladimir Nemirovich-Danchenko the Moscow Art Theatre (MAT) and began his professional career. The two of them were resolved to institute a revolution in the staging practices of the time. Benedetti offers a vivid portrait of the poor quality of mainstream theatrical practice in Russia before the MAT:

The script meant less than nothing. Sometimes the cast did not even bother to learn their lines. Leading actors would simply plant themselves downstage centre, by the prompter's box, wait to be fed the lines then deliver them straight at the audience in a ringing voice, giving a fine display of passion and "temperament." Everyone, in fact, spoke their lines out front. Direct communication with the other actors was minimal. Furniture was so arranged as to allow the actors to face front.

Stanislavski's early productions were created without the use of his system. His first international successes were staged using an external, director-centred technique that strove for an organic unity of all its elements—in each production he planned the interpretation of every role, blocking, and the mise en scène in detail in advance. He also introduced into the production process a period of discussion and detailed analysis of the play by the cast. Despite the success that this approach brought, particularly with his Naturalistic stagings of the plays of Anton Chekhov and Maxim Gorky, Stanislavski remained dissatisfied.

Both his struggles with Chekhov's drama (out of which his notion of subtext emerged) and his experiments with Symbolism encouraged a greater attention to "inner action" and a more intensive investigation of the actor's process. He began to develop the more actor-centred techniques of "psychological realism" and his focus shifted from his productions to rehearsal process and pedagogy. He pioneered the use of theatre studios as a laboratory in which to innovate actor training and to experiment with new forms of theatre.

Throughout his career, Stanislavski subjected his acting and direction to a rigorous process of artistic self-analysis and reflection. His system of acting developed out of his persistent efforts to remove the blocks that he encountered in his performances, beginning with a major crisis in 1906.