Bottom-Up Testing is a software testing approach that starts by testing individual components or modules of a system before integrating them into a larger system. This method focuses on verifying the functionality of the lower-level components first, ensuring that each part works correctly in isolation. Once these components are validated, they are gradually combined and tested together. This testing strategy is particularly useful in component-based development, where systems are built using reusable modules. By identifying and fixing issues at the component level, Bottom-Up Testing helps improve the overall quality of the software and reduces the risk of defects in the integrated system.