This handbook systematically collects latest scientific and technological knowledges on liquid metals obtained so far in this cutting edge frontier. Conventional materials like metals, polymers, composites, ceramics and naturally derived matters, may not work well when facing certain technological challenges. At around room temperature, most of such materials mainly stay at solid state and are often difficult to shape due to their high melting point. Meanwhile, although classical soft matters own good flexibility, their electrical conductivities including more behaviours appear not good enough which generally limited their utilizations. As a game changing alternative, the room temperature liquid metal materials are quickly emerging as a new generation functional material which displayed many unconventional properties superior to traditional materials. Their outstanding versatile feature as “One material, diverse capabilities” is rather unique among existing materials and thus opens many exciting opportunities for scientific, technological and industrial developments. This handbook presents comprehensive reference information for liquid metal sciences and technologies that are currently available. The major advancements as made before will be collected and summarized. Representative liquid metal applications will be illustrated. It will help readers obtain a comprehensive understanding of the technical progresses and fundamental discoveries in the frontier, and thus better investigate and utilize liquid metal materials to tackle various challenging needs.