Cosmological models are theoretical frameworks that describe the large-scale structure and evolution of the universe. They help scientists understand how the universe began, its current state, and its potential future. Key models include the Big Bang Theory, which suggests the universe started from a singular point and has been expanding ever since, and the Steady State Theory, which posits that the universe is eternal and maintains a constant average density. These models rely on observations from various sources, such as cosmic microwave background radiation and the distribution of galaxies. They also incorporate principles from general relativity and quantum mechanics to explain phenomena like dark matter and dark energy, which influence the universe's expansion.