An energy harvester connected to receive an electric current output at respective conducting pins of an integrated circuit package by a thermoelectric structure incorporated therein, wherein: the integrated circuit package comprises: a housing; an integrated circuit contained within the housing; the thermoelectric structure having a first face arranged in proximity to the integrated circuit within the housing and a second face arranged in thermal contact with ambient conditions; the electrically conducting pins extending outwardly from the housing and connected to the thermoelectric structure within the housing for conducting an electric current generated by the thermoelectric structure for use outside the package; and the energy harvester comprises a controller configured to control a use made of the received electric current; wherein the controller is configured to determine whether: (i) to use the received current to recharge an electrical energy storage device; or (ii) to use the received current as a supplementary source of electric current for operation of the integrated circuit package or for another electronic device; or (iii) to supply previously stored energy from the electrical energy storage device; and wherein the controller is configured to receive a sensed temperature indication from a temperature sensor associated with the integrated circuit package and, if the sensed temperature exceeds a predetermined upper limit, to trigger the supply of an electric current to the thermoelectric structure provided in the package via the respective conducting pins and thereby provide cooling of an integrated circuit incorporated within the package. the integrated circuit package comprises: a housing; an integrated circuit contained within the housing; the thermoelectric structure having a first face arranged in proximity to the integrated circuit within the housing and a second face arranged in thermal contact with ambient conditions; the electrically conducting pins extending outwardly from the housing and connected to the thermoelectric structure within the housing for conducting an electric current generated by the thermoelectric structure for use outside the package; and the energy harvester comprises a controller configured to control a use made of the received electric current; wherein the controller is configured to determine whether: (i) to use the received current to recharge an electrical energy storage device; or (ii) to use the received current as a supplementary source of electric current for operation of the integrated circuit package or for another electronic device; or (iii) to supply previously stored energy from the electrical energy storage device; and (i) to use the received current to recharge an electrical energy storage device; or (ii) to use the received current as a supplementary source of electric current for operation of the integrated circuit package or for another electronic device; or (iii) to supply previously stored energy from the electrical energy storage device; and wherein the controller is configured to receive a sensed temperature indication from a temperature sensor associated with the integrated circuit package and, if the sensed temperature exceeds a predetermined upper limit, to trigger the supply of an electric current to the thermoelectric structure provided in the package via the respective conducting pins and thereby provide cooling of an integrated circuit incorporated within the package.