This review paper presents the main energy storage system (ESS) technologies used in non-interconnected European islands, along with their technical and life cycle analysis, and the range of ancillary services they can provide. It also provides a detailed description of existing ESS installations or combinations in non-interconnected European islands. The paper aims to map the current status of storage solutions that enhance the sustainable and environmentally friendly operation of autonomous systems. The main ESS technologies are classified into electrochemical, mechanical, and thermal. Electrochemical ESSs include batteries, supercapacitors, and fuel cells. Mechanical ESSs include hydro-pumped storage, flywheels, and compressed air energy storage (CAES). Thermal ESSs include thermal energy storage (TES) systems. Each technology has its own advantages and disadvantages, and the choice of ESS depends on the specific needs of the system. ESSs can provide various ancillary services, including frequency-related services such as virtual/synthetic inertia, fast frequency response (FFR), frequency containment reserve (FCR), and frequency restoration reserve (FRR), as well as non-frequency-related services such as voltage regulation, network congestion mitigation, and short-circuit current management. Additionally, ESSs can provide islanding and black-start services, which are crucial for non-interconnected systems. The paper also presents examples of ESS installations in non-interconnected European islands, including the hydro-pumped storage system in Ikaria, Greece, and various battery and hybrid systems in Portuguese islands such as Terceira, Madeira, and Porto Santo. Other examples include the Faroe Islands, Italy, Spain, and the Canary Islands, where ESSs are used to support renewable energy integration and grid stability. The review highlights the importance of ESSs in non-interconnected systems, where the integration of renewable energy sources (RES) can lead to challenges in power quality and system stability. ESSs help mitigate these challenges by providing ancillary services and supporting the operation of the power system. The paper concludes that ESSs are essential for the sustainable and environmentally friendly operation of non-interconnected systems, and their selection and implementation depend on the specific needs of the system.This review paper presents the main energy storage system (ESS) technologies used in non-interconnected European islands, along with their technical and life cycle analysis, and the range of ancillary services they can provide. It also provides a detailed description of existing ESS installations or combinations in non-interconnected European islands. The paper aims to map the current status of storage solutions that enhance the sustainable and environmentally friendly operation of autonomous systems. The main ESS technologies are classified into electrochemical, mechanical, and thermal. Electrochemical ESSs include batteries, supercapacitors, and fuel cells. Mechanical ESSs include hydro-pumped storage, flywheels, and compressed air energy storage (CAES). Thermal ESSs include thermal energy storage (TES) systems. Each technology has its own advantages and disadvantages, and the choice of ESS depends on the specific needs of the system. ESSs can provide various ancillary services, including frequency-related services such as virtual/synthetic inertia, fast frequency response (FFR), frequency containment reserve (FCR), and frequency restoration reserve (FRR), as well as non-frequency-related services such as voltage regulation, network congestion mitigation, and short-circuit current management. Additionally, ESSs can provide islanding and black-start services, which are crucial for non-interconnected systems. The paper also presents examples of ESS installations in non-interconnected European islands, including the hydro-pumped storage system in Ikaria, Greece, and various battery and hybrid systems in Portuguese islands such as Terceira, Madeira, and Porto Santo. Other examples include the Faroe Islands, Italy, Spain, and the Canary Islands, where ESSs are used to support renewable energy integration and grid stability. The review highlights the importance of ESSs in non-interconnected systems, where the integration of renewable energy sources (RES) can lead to challenges in power quality and system stability. ESSs help mitigate these challenges by providing ancillary services and supporting the operation of the power system. The paper concludes that ESSs are essential for the sustainable and environmentally friendly operation of non-interconnected systems, and their selection and implementation depend on the specific needs of the system.