From their very inception, movies have served two seemingly contradictory purposes. On one hand, they transport us to fantastical worlds and display mind-boggling special effects. On the other, they can document actual events and immerse us in scenarios that feel so realistic, we might forget we are watching a work of fiction. Alternative Realities explores how these distinctions between cinematic fantasy and filmic realism are more porous than we might think. Through a close analysis of CGI-heavy blockbusters like Wonder Woman and Guardians of the Galaxy, it considers how even popular fantasies are grounded in emotional and social realities. Conversely, it examines how mockumentaries like This is Spinal Tap satirically call attention to the highly stylized techniques documentarians use to depict reality. Alternative Realities takes us on a journey through many different genres of film, from the dream-like and subjective realities depicted in movies like Eternal Sunshine of the Spotless Mind and Memento, to the astonishing twists of movies like Shutter Island and The Matrix, which leave viewers in a state of epistemic uncertainty. Ultimately, it shows us how the power of cinema comes from the unique way it fuses together the objective and the subjective, the fantastical and the everyday.