Abstract: Diffuse aurora is a natural light display in the sky and occurs over an extensive polar region of magnetized planets in our solar system. Earth’s diffuse auroral precipitation is known to provide the main source of energy for the high-latitude nightside upper atmosphere, leading to enhanced ionization and chemical changes. Although diffuse aurora is generally known to be excited by downward-streaming electrons into the upper atmosphere, identifying the driver of the electron precipitation has been a long-standing problem. The recent satellite missions including THEMIS and Van Allen Probes, as well as all-sky imagers on the ground, have provided an unprecedented opportunity to explore the origin of diffuse aurora at Earth. Moreover, Juno mission, the first spacecraft to explore the polar regions of Jupiter, has provided a unique opportunity to understand the characteristics and origin of diffuse aurora at Jupiter. In this colloquium, I will discuss the recent advances in understanding the physical process of driving diffuse aurora at Earth. Then I will present how we apply what we have learned from Earth to understand Jupiter’s diffuse aurora, and discuss the similarities and differences of diffuse aurora at Earth and Jupiter in a comparative way. At last, I will talk about the challenges and open questions regarding diffuse aurora, followed by exciting future opportunities.