This book aims to overview the variety of efficient applications of free POM and POM-based (nano)composites as exciting materials for electrocatalysis. It covers the general methodologies used in the preparation of free POMs and POM-based nanocomposites the different strategies employed in electrode modification. The second and third part discuss the role of POM-modified electrodes in oxidative and reductive electrocatalysis including the detection/sensing of several (bio)molecules of interest and the carbon dioxide electroreduction. The fourth and fifth part focuses on the application of POM-based (nano)composites as electrocatalysts for energy-related reactions relevant to renewable energy storage and conversion technologies. These include the oxygen reduction reaction relevant to fuel cells, the oxygen and hydrogen evolution reactions, batteries and supercapacitors. It includes challenges an future prospective of POM and POM-based materials electrocatalytic applications.