Fault injection is a technique used to introduce deliberate failures into systems to test their resilience, originating from hardware testing where engineers subjected devices to harmful conditions to gauge their functionality under stress. Over time, this practice evolved into software fault injection, allowing engineers to simulate faults in applications and test error-handling mechanisms. Notably, Netflix's Chaos Monkey and Failure Injection Testing (FIT) platform popularized the application of fault injection in cloud infrastructures, laying the groundwork for modern Chaos Engineering. Chaos Engineering extends fault injection by using it strategically to observe system responses to controlled failures, thereby enhancing reliability. Tools like Gremlin support this by offering structured failure simulations, helping organizations uncover and address potential failure modes, validate monitoring and incident response processes, and reduce the risk of production outages. Ultimately, fault injection aims to improve system reliability by identifying vulnerabilities that traditional testing might miss and preparing teams to effectively handle real-world failures.