Many processes are required throughout the aircraft's operating life to ensure that it complies with the applicable airworthiness requirements and can be safely operated. The generic term for this range of processes is continuing airworthiness. The term 'maintenance' is used for any combination of overhaul, repair, inspection, replacement, modification or defect rectification of an aircraft or component, with the exception of the pre-flight inspection. Persons responsible for the release of an aircraft or a component after maintenance are the certifying staff. Maintenance of an aircraft and its associated systems requires a variety of test equipment and documentation; these are required by certifying staff to fulfil their obligations in ensuring continued airworthiness. Aircraft wiring cannot be considered as 'fit and forget'. Legislation is being proposed to introduce a new term: electrical wire interconnection system {EWIS); this will acknowledge the fact that wiring is just one of many components installed on the aircraft. EWIS relates to any wire, wiring device, or combination of these, including termination devices, installed in the aircraft for transmitting electrical energy between two or more termination points. This chapter reviews some practical installation requirements, documentation and test equipment required by the avionics engineer to ensure the continued airworthiness of aircraft electrical and electronic systems.