The past decade has witnessed a burst of study on ultrasmall gold nanoparticles. Unlike semiconductor quantum dots, ultrasmall gold nanoparticles have very diverse emission mechanisms, which are often involved in many structural factors such as size, valence state, surface ligands and crystallinity. In this frontier, we summarize our latest advancement in the fundamental understanding of emission mechanisms of ultrasmall gold nanoparticles, which are expected to help us more precisely control their emissions and broaden their applications from energy technologies to disease detection.