Aggregates are a fundamental component in asphalt mixtures and highway construction, significantly influencing the structural integrity, durability, and performance of pavements. The study of aggregates encompasses their origin, classification, and physical characteristics, including distinctions between natural and manufactured sources. A geological overview of igneous, sedimentary, and metamorphic rocks provides context for the selection of appropriate aggregate types for specific engineering applications. A detailed examination of aggregate properties—such as gradation, shape, texture, strength, abrasion resistance, soundness, polishing resistance, specific gravity, absorption, and alkali-aggregate reactivity—is presented alongside standard test methods used to evaluate these parameters. Emphasis is placed on the importance of proper aggregate gradation and blending to achieve optimal mixture performance. Key methodologies discussed include the traditional gradation approach, the Stone-on-Stone Contact method, the Power Law Method, and the Bailey Method. The phenomenon of aggregate segregation is analyzed in depth, including its types, causes, and effects on pavement quality. Practical strategies for minimizing segregation during mix design, stockpiling, handling, and plant operations are also outlined. A comprehensive understanding of these principles is essential for producing high-quality, long-lasting asphalt pavements capable of withstanding traffic and environmental stresses.