Theodore Twombly (Phoenix) has built his career on expressing the emotions that others cannot. His job is to pen heartfelt, deeply personal letters to complete strangers based on details provided by the clients of the company he works for, and he has a knack for finding just the right words for every occasion. Meanwhile, reluctant to sign the papers that will finalize his divorce to his childhood sweetheart, depressed Theodore has slowly withdrawn from his supportive social circle, which includes his longtime friend Amy (Amy Adams), herself floundering in a failed marriage. When Theodore purchases a new state-of-the-art computer operating system with the ability to learn and grow with the user, he sits down at his desk and prepares to get his life in order. Adopting the name Samantha (Scarlett Johansson), the perceptive software slowly begins to bring Theodore out of his shell by encouraging him to start dating again, and joining him everywhere he goes. Very quickly, their relationship turns intimate, with Theodore teaching Samantha what it means to feel human and Samantha giving him the strength to walk away from his failed marriage. Things soon get complicated, however, when Samantha's rapidly evolving knowledge base begins to alter the very core of their relationship.