Identity resolution is the process of combining different technologies, data sources, and signals to create a consistent record for entities like people and products. It aims to provide deep consumer insights that allow for personalized digital experiences and enables targeted advertising. Identity resolution combines first-party and third-party data into a single identity that can be used for targeting or personalization and is tracked across any device the user uses while respecting consumer privacy and safety. The process involves data onboarding, matching external identifiers with online identifiers, and building complex probabilistic models to link data points to customer entities. Modern approaches prioritize first-party data, cleanrooms, and advanced technologies like graph databases, machine learning, and data processing to ensure accurate and private identity resolution. Despite advancements, challenges such as data inconsistencies, shared identifiers, data volumes, deterministic vs. probabilistic identity resolution, regulatory differences, and walled gardens remain, making the future of identity resolution complex, technical, and expensive.