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Power supply utilities are continuously working to maintain reliable and efficient electrical networks that meet the growing demand for electricity. This is a complex task in which appropriate maintenance, refurbishment and replacement policies for all the assets are critical. Optimising business processes through these constitutes a key challenge of balancing service quality and stakeholder value. Here we present two frameworks that can be used to effectively condition monitor both ethylene propylene diene monomer (EPDM) and silicone rubber (SiR) composite insulators during their lifetime in service. The frameworks are tools to assist asset management decision making. The first framework is derived from a generalized dielectric ageing framework and a more specific one on composite insulators that points out the elements that govern composite insulator materials¿ ageing on power transmission and distribution lines. The second framework defines four aged states in relation to the risk to failure that a composite insulator has in service before its replacement. Properties of materials that can be measured in order to identify ageing are reviewed. The techniques available as engineering tools for measuring these properties are introduced. These are distinguished as techniques that can be carried out on-line and off-line, and as destructive and non-destructive tests. These techniques are then reviewed in the context of monitoring and maintaining reliable and efficient operation of power networks.