Quantum sensors offer unprecedented opportunities for precision measurements, with far-reaching implications for both fundamental scientific and technological applications. In this talk, we will present a broad overview of the evolving scientific landscape, highlighting how quantum-enabled techniques are driving advances across a range of cutting-edge sensing applications such as biomedical imaging. We will illustrate, through examples selected from our recent research, how fundamental quantum phenomena—e.g., quantum noise, many-body correlation, and environmental decoherence—fundamentally determine the performance limits of quantum sensors.