The Hook Model is a framework developed by Nir Eyal to explain how products can create user habits. It consists of four key components: Trigger, Action, Variable Reward, and Investment. These elements work together to encourage users to engage repeatedly with a product or service. Triggers prompt users to take action, while the action itself is the behavior they perform. After the action, users receive a variable reward, which keeps them engaged due to its unpredictability. Finally, investment refers to the effort users put into the product, increasing the likelihood of future engagement.