Quantum entanglement is perhaps the most weird phenomenon in our physical world. The realization of this effect in experiments have drastically influenced our thoughts about universe. Nevertheless entanglement promises to provide us with new modes of computation and secure communication. Quantum cryptography, quantum teleportation, quantum dense coding, etc, depend on utilization of entanglement. However, it was noted that in certain cases entanglement vanishes from physical systems after a very short time. This strange observation has been named entanglement sudden death. This book examines entanglement and the processes which are responsible for its sudden death. We also discuss the methods to avoid, hasten or at least delay the unwanted effect of entanglement sudden death.