1. Initiation: This is the step where a free radical or other reactive species is generated. This can be done by a variety of means, such as heating, irradiation, or the addition of a catalyst.

2. Propagation: This is the step where the free radical or other reactive species reacts with another molecule to produce two new free radicals or reactive species. This process can continue in a chain reaction, with each new free radical or reactive species reacting with another molecule to produce two more free radicals or reactive species.

3. Termination: This is the step where the chain reaction is stopped. This can happen when two free radicals or reactive species react with each other to form a stable product, or when a free radical or reactive species reacts with an inhibitor.