Measurement device independent quantum key distribution (MDI-QKD) is a method to securely distribute cryptographic keys over long distances by eliminating detector side-channel attacks. This approach uses phase-randomized weak coherent pulses (WCPs) and an untrusted relay to perform a Bell state measurement, ensuring security even with flawed detectors. MDI-QKD doubles the secure transmission distance compared to conventional QKD systems and offers a higher key generation rate than full device independent QKD. It requires only standard optical components with low detection efficiency and highly lossy channels, making it practical for real-world applications. The protocol involves Alice and Bob preparing WCPs in different polarization states, sending them to an untrusted relay, and performing a Bell state measurement. The relay then announces successful outcomes, allowing Alice and Bob to post-select events and generate a secure key. The protocol is secure against detector side-channel attacks and can tolerate high optical losses, making it suitable for long-distance quantum communication. MDI-QKD has been experimentally demonstrated, showing high-visibility Hong-Ou-Mandel interference between two independent lasers, confirming its feasibility. The method is simple to implement and offers significant advantages over existing QKD protocols, bridging the gap between theoretical security and practical implementation.Measurement device independent quantum key distribution (MDI-QKD) is a method to securely distribute cryptographic keys over long distances by eliminating detector side-channel attacks. This approach uses phase-randomized weak coherent pulses (WCPs) and an untrusted relay to perform a Bell state measurement, ensuring security even with flawed detectors. MDI-QKD doubles the secure transmission distance compared to conventional QKD systems and offers a higher key generation rate than full device independent QKD. It requires only standard optical components with low detection efficiency and highly lossy channels, making it practical for real-world applications. The protocol involves Alice and Bob preparing WCPs in different polarization states, sending them to an untrusted relay, and performing a Bell state measurement. The relay then announces successful outcomes, allowing Alice and Bob to post-select events and generate a secure key. The protocol is secure against detector side-channel attacks and can tolerate high optical losses, making it suitable for long-distance quantum communication. MDI-QKD has been experimentally demonstrated, showing high-visibility Hong-Ou-Mandel interference between two independent lasers, confirming its feasibility. The method is simple to implement and offers significant advantages over existing QKD protocols, bridging the gap between theoretical security and practical implementation.