<p>Bitumen aging occurs primarily due to the rheological, morphological and chemical changes in bitumen matrix driven by the synergistic impact of thermal-oxidative processes, UV irradiation, and moisture in the field. Aging results in increased stiffness and viscosity, limiting its ability to accommodate traffic and thermal stresses, which accelerates pavement failures such as fatigue, thermal cracking and ravelling, thereby reducing the longevity of flexible pavements. Quantifying aging of bitumen is critical for selecting and formulating effective bitumen for applications in flexible pavements. This study aims to present a thorough analysis of bitumen aging, the different aging mechanisms that are encountered in the field such as UV aging, short-term aging, long-term aging, and the various aging indicators, as well as the rheological, spectroscopic, and chromatographic methods that are widely used to assess how aging affects the rheological, chemical, and morphological properties of bitumen. Additionally, it reviews the most widely adopted bitumen modification strategies aimed at improving aging resistance and their influence on long-term performance. Furthermore, the study intends to thoroughly evaluate the current state of scientific development in this area, identify knowledge gaps, and highlight aspects that require further investigation, particularly regarding the existing aging simulation techniques and the need for standardized techniques to simulate the synergic field aging phenomenon in bitumen.</p>