Piezoelectric ultrasonic transducers have shown great potential in biomedical applications due to their high acoustic-to-electric conversion efficiency and large power capacity. The focusing technique enables the transducer to produce an extremely narrow beam, greatly improving the resolution and sensitivity. In this work, we summarize the fundamental properties and biological effects of the ultrasound field, aiming to establish a correlation between device design and application. Focusing techniques for piezoelectric transducers are highlighted, including material selection and fabrication methods, which determine the final performance of piezoelectric transducers. Numerous examples, from ultrasound imaging, neuromodulation, tumor ablation to ultrasonic wireless energy transfer, are summarized to highlight the great promise of biomedical applications. Finally, the challenges and opportunities of focused ultrasound transducers are presented. The aim of this review is to bridge the gap between focused ultrasound systems and biomedical applications.