A state retention circuit is provided comprising a pulse generator which is configured in a non-retention mode of operation to be responsive to a clock signal to periodically assert a pulse, and a storage structure that comprises a storage element for storing state and an isolation structure for responding to the asserted pulse. In particular, the isolation structure is responsive to the asserted pulse to cause the storage element to update its stored state dependent on an input to the storage structure. Conversely, in the absence of the asserted pulse, the isolation structure isolates the storage element from the input. The pulse generator can be driven by a retention control signal to enter a retention mode of operation, during which it does not assert the pulse irrespective of changes in the clock signal. As a result, the isolation structure isolates the storage element from the input during the retention mode of operation, causing the storage element to retain its stored state prior to entry of the retention mode of operation irrespective of changes in the clock signal or changes in the input during the retention mode of operation. Such a design provides a clock independent pulse retention storage structure of small area, high performance and low energy consumption.