There are difficulties to guarantee QoS of mobile Ad Hoc networks due to their features of dynamically changing topology and wireless communication. Current QoS techniques for mobile Ad Hoc networks are divided into five categories: link layer solutions, network layer solutions, transport layer solutions, cross layers solutions and cross networks solutions. The main link layer solutions are QoS MAC protocols. The main idea in network layer solutions is QoS routing. Wireless TCP is the main scheme to guarantee QoS in transport layer. To choose route and balance load, cross layer solutions were researched to provide network architectures to support QoS. The main idea in cross network solutions is to propose QoS solutions between mobile Ad Hoc networks and fixed networks. These QoS solutions were introduced and analyzed.