Aerosol Jet Printing (AJP) is an emerging contact-free direct writing approach, aiming at producing fine features on various types of substrates. Originally, the technology was developed for manufacturing electronic circuits and has been explored for various applications, including active and passive electronic components, actuators, sensors, as well as a variety of components to detect selective chemical and biological responses. This article will cover the design of aerosol jet printing system, its research progress in circuit repair, and corresponding results.