Liquid metal marbles that are droplets of liquid metal encapsulated by micro- or nanoparticles are introduced. Droplets of galinstan liquid metal are coated with insulators (including Teflon and silica) and semiconductors (including WO3, TiO2, MoO3, In 2O3 and carbon nanotubes) by rolling over a powder bed and also by submerging in colloidal suspensions. It is shown that these marbles can be split and merged, can be suspended on water, and are even stable when moving under the force of gravity and impacting a flat solid surface. Furthermore, the marble coating can operate as an active electronic junction and the nanomaterial coated liquid metal marble can act as a highly sensitive electrochemical based heavy metal ion sensor. This new element thus represents a significant platform for the advancement of research into soft electronics. Liquid metal marbles are formed by encapsulating droplets of liquid metal in micro/nanoparticles that are insulating or semiconducting. The physical properties of the liquid metal marbles are investigated. The ability to form active electronic junctions using liquid metal marbles and its use as a highly sensitive, electrochemical-based, heavy metal ion sensor is demonstrated. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.