Constantin Stanislavski was a Russian actor and theater director born to wealthy parents in 1863. Often called the "Father of Method Acting," he encouraged his students to research their roles and to use their imaginations to create emotions on stage as opposed to the study of a set of stylized reactions that were routinely memorized in theater. Students of Stanislavski's methods learn to break down the objectives and identify the obstacles for the characters in any given situation. Emotional memory is also stressed in this method, with students encouraged to recall emotions based on a particular event in their personal past and using it to their advantage on stage.
Drawing on the works of the established works of Stanislavski, Lee Strasberg of The Actor's Studio encouraged his students to immerse themselves completely in their characters. In this particular school of study, the students learn to remove the stress in their bodies including any muscular tension in order to "free" the actor's instrument from any impediments of expression and to improve their concentration. Sensory memory is crucial in studying Method acting. Beginners are expected to examine everyday objects and be able to recall every aspect of the item to train them to remember what any given situation was truly like.
Sanford Meisner was an American actor who studied with Lee Strasberg in New York and cultivated a method that molded both Stanislavski's methods with Strasberg's to form what was to be known as the Meisner Technique. This technique stresses an actor's involvement in what he is actually doing on stage and that the actor achieves realism through doing what the character would do. Students are encouraged to live in the moment and to use their imaginations and to prepare for their role through careful research. This method stresses learning lines in advance in a mechanical and rote fashion and saving inflections and interpretations for the actual performance.
The film star and renowned acting teacher Stella Adler was the only American actor to study with Stanislavski. If you study the Adler technique, you will learn that acting is doing and to look for things in the script that will help you perform an action. Adler believed in developing the imagination and then training the mind to have a real understanding of the play. Unique to the Adler technique is the concept of size -- that actors need strong bodies and voices for the stage so they can bring a sense of size to their action and a "sense of the epic."