This paper presents a Hierarchical Identity Based Encryption (HIBE) system with constant size ciphertexts. The system allows encryption with only three group elements and decryption using two bilinear map computations, regardless of the hierarchy depth. The scheme is selective-ID secure in the standard model and fully secure in the random oracle model. It has several applications, including efficient forward secure encryption, converting the NNL broadcast encryption system into a public key broadcast system, and providing an efficient mechanism for encrypting to the future. The system also supports limited delegation, where users can be given restricted private keys that only allow delegation to bounded depth. The HIBE system can be modified to support sublinear size private keys at the cost of some ciphertext expansion. The system is based on a natural assumption related to the Diffie-Hellman Inversion assumption. The paper also discusses extensions and applications of the system, including limited delegation, HIBE with short private keys, and encrypting to the future. The system is proven secure under the decisional Bilinear Diffie-Hellman Exponent assumption. The paper concludes with a discussion of future research directions.This paper presents a Hierarchical Identity Based Encryption (HIBE) system with constant size ciphertexts. The system allows encryption with only three group elements and decryption using two bilinear map computations, regardless of the hierarchy depth. The scheme is selective-ID secure in the standard model and fully secure in the random oracle model. It has several applications, including efficient forward secure encryption, converting the NNL broadcast encryption system into a public key broadcast system, and providing an efficient mechanism for encrypting to the future. The system also supports limited delegation, where users can be given restricted private keys that only allow delegation to bounded depth. The HIBE system can be modified to support sublinear size private keys at the cost of some ciphertext expansion. The system is based on a natural assumption related to the Diffie-Hellman Inversion assumption. The paper also discusses extensions and applications of the system, including limited delegation, HIBE with short private keys, and encrypting to the future. The system is proven secure under the decisional Bilinear Diffie-Hellman Exponent assumption. The paper concludes with a discussion of future research directions.