Most mobile Augmented Reality (AR) systems use either a head mounted display (HMD) or a handheld display (HHD) as a hardware platform. As mobile devices become more affordable, it becomes more common that users own more than one mobile device and use them together. In this research, we investigate Hybrid AR systems that use both HMD and HHD for AR visualization and interaction. In addition to a simple approach of using HMD as a display and HHD as an input device (e.g. a touch pad or a pointer), we further explore novel interaction techniques that can take advantage of having both HMD and HHD closely integrated into one AR system, such as cross-device information sharing, situation adaptive visualization management, and multilayered visualization.