This book presents an integrated study of perovskite-based chemiresistive gas sensors, combining Density Functional Theory (DFT) modeling and experimental validation to establish a comprehensive understanding of gas–surface interactions. The research focuses on Bismuth Ferrite (BiFeO₃) and its Ag-doped variants, highlighting their potential as efficient, low-cost materials for detecting toxic automotive and industrial gases such as CO, NO, NO₂, and SO₂. Beginning with the fundamental principles of perovskite oxides, the book explores the electronic structure, adsorption energetics, and charge transfer mechanisms of BFO surfaces using DFT simulations. These theoretical insights are then linked to experimental studies involving the synthesis, structural and spectroscopic characterization, and gas sensing performance of pure and Ag-doped BFO films. Through systematic analysis, the work demonstrates how Ag doping enhances adsorption, sensitivity, and selectivity, while reducing operating temperatures. The book concludes with perspectives on future advancements in nanostructured gas sensors, AI-assisted sensing arrays, and hybrid material systems. This volume is a valuable resource for researchers, engineers, and graduate students working in materials science, nanotechnology, solid-state physics, and environmental monitoring.