Vibration is ubiquitous in the human body and its surrounding environment. Many internal physiological processes in our body produce subtle vibrations with different frequencies, which carry representative information about the state of our health. Similarly, characteristics of externally induced vibrations in our surrounding material environment can be indicative of whether any materials or chemicals can pose threats to our health. In my research, I exploit acoustic waves, electromagnetic waves, and their interactions to develop mobile systems that passively and unobtrusively listen to underlying health signals. Despite the rapid growth of mobile health applications in recent years, many of these health sensing modalities remain largely untapped. In this dissertation, I will present my recent and ongoing research to demonstrate how naturally generated and backscattered acoustic and electromagnetic waves from the human body (e.g., heart, lung, skin) and its surrounding material environment (e.g., food) can be used to infer intermediate health signals like physiological acoustics, vital signs, and spectral properties of materials. I will also describe how these signals can be mapped to high-level health and behavioral variables including non-speech body sound, sleep stages, and food quality. Finally, I will lay out my future plans to develop low-cost next-generation mobile health systems for individualized and community-wide healthcare.