Retrofitting refers to the addition of new technology or features to older systems.

• power plant retrofit, improving power plant efficiency / increasing output / reducing emissions
• home energy retrofit, the improving of existing buildings with energy efficiency equipment
• seismic retrofit, the process of strengthening older buildings in order to make them earthquake resistant
• Naval vessels often undergo retrofitting in dry dock to incorporate new technologies, change their operational designation, or compensate for perceived weaknesses in their design or gun plan.