Expert systems are a branch of artificial intelligence that emerged prominently in the 1970s and 1980s. These systems are designed to mimic the decision-making ability of a human expert, utilizing a knowledge base and a set of rules to solve complex problems in specific domains such as medical diagnosis or financial forecasting. A famous example is MYCIN, developed at Stanford University, which was designed to diagnose bacterial infections and recommend antibiotics. Despite their early promise, expert systems faced limitations due to their reliance on rigid rule-based structures, leading to the evolution of more flexible AI technologies.