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Inflation was originally conceived as an elegant solution to the horizon, flatness, and relic problems of standard cosmology, with single-field models long favored for their simplicity and predictive power. However, developments in high-energy theory increasingly motivate scenarios with multiple interacting scalar fields. Multifield inflation introduces new conceptual elements, including field-space geometry, entropy perturbations, and non-geodesic dynamics, which can significantly affect inflationary predictions. This conceptual paper examines the foundational shift from single-field to multifield inflation, highlighting how multifield models provide novel mechanisms for generating cosmological relics, such as primordial black holes (PBHs) and nonthermal dark matter (DM). Once viewed as an artificial complication, multifield inflation now emerges as a conceptually rich and observationally testable paradigm for early universe cosmology.