The recent decade witnessed a dizzying pace of developments in the micromachined ultrasonic transducers and systems. Driven by emerging applications like fingerprint sensing and portable medical ultrasound systems, and supported by the advances in process development and batch manufacturing, Piezoelectric (PMUT) and capacitive (CMUT) technologies finally started to become commercially viable. A common denominator of these successful applications is ultrasonic MEMS/electronics integration where ultrasonic MEMS has distinct advantages over conventional ultrasound transducer technology. In this talk, we will first review the CMUT and PMUT technologies in terms of fabrication process, transducer characteristics and applications. We will then focus on electronics integration as an enabling factor to exploit distinct advantages of ultrasonic MEMS such as low noise, broad bandwidth and miniaturization for imaging and sensing. Finally, we will provide several examples of our work on CMUT-CMOS electronics integrated systems for catheter based medical imaging and discuss potential future applications of ultrasonic MEMS.