Regression testing is a critical component of software development that ensures that new code changes, bug fixes, or enhancements do not introduce new defects into existing software functionality. This type of testing is performed after code modifications to verify that the changes have not adversely affected the system. Regression testing can be executed manually or through automation, using various techniques such as Corrective, Unit, Selective, Progressive, Complete, Partial, and Retest-all methods. It is essential for maintaining software quality and stability, enabling developers to detect and resolve issues early, thus reducing risks and improving customer satisfaction. Despite its challenges, such as time and resource consumption, regression testing is indispensable in agile development environments, and tools like Selenium and LambdaTest can streamline the process by providing automated solutions that enhance efficiency and scalability.