As the original inventors, it is fascinating to witness that scaling the size of standard light emitting diodes (LEDs) down to micron length scales has created such immense new research and commercialization opportunities. Today, microLED is recognized as the ultimate display technology and is one of the fastest-growing technologies in the world as technology giants utilize it on a wide range of products from large flat panel displays and televisions, wearable displays, 3D/augmented reality/virtual reality (3D/AR/VR) displays, to light source for neural interface and optogenetics. This chapter provides a brief review of early and recent developments and current challenges in research, applications, and prospective uses of microLEDs. The basic III-nitride microLED material structures, fabrication processes and characteristics are discussed. The realization of the first active driving InGaN full-sale high-resolution monochrome microdisplay in video graphics array format (640 × 480 pixels) capable of delivering video graphics images is described. The invention of single-chip high-voltage AC- and DC LEDs based on microLED or mini-LED array technology for general illumination and solid-state lighting applications is reviewed. Recent efforts toward the realization of full color microdisplays are examined. It is anticipated that the collective R&D efforts worldwide will bring microLED products not only to the mass consumer electronics markets, but also to serve the society on the broadest scale by encompassing sectors in medical/health, energy, transportation, communications, and entertainment.