The localization and time synchronization of Underwater Acoustic Devices (UADs) have many potential applications in industry and scientific research. This can be done by deploying location-aware fixed anchors on the sea surface or bottom. However, this solution has poor accuracy and induces huge costs. In recent years, with the surge of Autonomous Underwater Vehicles (AUVs), the possibility of employing smart AUVs as mobile anchors have been extensively discussed. In this chapter, three smart AUV-assisted underwater localization and time synchronization techniques will be introduced, based on ToA (Time of Arrival), Doppler shift, and linear frequency modulated signals. The system model will be presented in detail, and the corresponding algorithms will be briefly discussed. For each of them, some preliminary numerical evaluations are conducted to directly show their performance.