Encrypted Search, a technique for securely searching documents on untrusted systems. The author designs and compares several secure index types to determine their performance in terms of time complexity, space complexity, and retrieval accuracy. The study also examines the risk to confidentiality posed by storing frequency and proximity information and suggests ways to mitigate the risk. Additionally, the author investigates the impact of false positives and secure index poisoning on performance and confidentiality. Finally, the thesis explores techniques to protect against adversaries with access to encrypted query histories, such as query obfuscation.