Polymers derived from plant oils have attracted major commercial interest and significant attention in scientific research because of the availability, biodegradability, and unique properties of triglycerides. Triglycerides rich in unsaturated fatty acids, such as soybean oil (SBO), are particularly susceptible to chemical modification for desired polymeric materials. Soy-based polyols are important industrial prepolymeric materials that use renewable resources; and can be produced or derived through different processing routes. This review paper discusses previous and recent researches about chemical and biochemical polymerization processes to produce soy-based polyols as prepolymers for the production of polyurethane materials in the form of foams (rigid or flexible) and elastomers. The central goal of these research fields is to find effective reaction routes to increase both equivalent weight and hydroxyl functionality of soy-based polyols while taking into consideration the simplicity and economics of these processes.