Bitumen is a complex viscoelastic material integral to modern road construction, owing to its binding capabilities, durability, and adaptability under varying environmental conditions. This chapter provides a comprehensive overview of bitumen, beginning with its chemical composition, microstructural characteristics, and historical evolution as a construction material. Key aspects such as the SARA fractionation (Saturates, Aromatics, Resins, and Asphaltenes), manufacturing processes, and the influence of polarity on physical behavior are elaborated to build a foundational understanding of its performance. Various types of bitumen—paving-grade binders, cutbacks, emulsions, and polymer-modified binders—are discussed along with their specific applications, advantages, and formulation methods. The chapter critically examines grading systems including penetration, viscosity, and performance grading (Superpave), highlighting their evolution, methodologies, limitations, and impact on pavement design and quality control. Special focus is given to modern advancements in bitumen modification through polymers, thermoplastics, thermosets, natural and synthetic rubber, chemical agents, and nanomaterials, detailing their effects on rheological properties, temperature susceptibility, aging resistance, and storage stability. Additionally, the role of warm mix asphalt technologies in enhancing sustainability and reducing energy consumption is analyzed. By integrating historical insights, technical evaluations, and cutting-edge developments, the chapter equips engineers, researchers, and practitioners with a thorough understanding of bitumen as a versatile and evolving material essential to sustainable and high-performance asphalt pavements.