A sensor-driven glucose control system, comprising: a glucose sensor continually operative to generate a measured glucose level signal indicative of a measured glucose level of a subject; an insulin delivery device operative in response to an insulin dose control signal to deliver doses of insulin for infusion into the subject; and a controller operative according to a control scheme to generate the insulin dose control signal in response to (a) the measured glucose level signal and (b) a target glucose level signal by: calculating corrective insulin doses based on the target glucose level signal and variations of the measured glucose level signal occurring on the order of seconds to minutes; and continually adjusting the target glucose level signal based on a calculated longer term trend represented by at least values of the measured glucose level signal over the longer term, wherein continually adjusting the target glucose level signal is based on a function of measured glucose levels over a recent period, characterised in that the function is a weighted sum computed using a scaling factor with which measured glucose levels are multiplied to determine offsets caused on the target glucose level signal by respective contributions from measured glucose levels, wherein the scaling factor varies depending on the respective measured glucose levels, wherein the scaling factor is a relatively low value for high values of measured glucose level and progressively higher for lower values of measured glucose level. a glucose sensor continually operative to generate a measured glucose level signal indicative of a measured glucose level of a subject; an insulin delivery device operative in response to an insulin dose control signal to deliver doses of insulin for infusion into the subject; and a controller operative according to a control scheme to generate the insulin dose control signal in response to (a) the measured glucose level signal and (b) a target glucose level signal by: calculating corrective insulin doses based on the target glucose level signal and variations of the measured glucose level signal occurring on the order of seconds to minutes; and continually adjusting the target glucose level signal based on a calculated longer term trend represented by at least values of the measured glucose level signal over the longer term, calculating corrective insulin doses based on the target glucose level signal and variations of the measured glucose level signal occurring on the order of seconds to minutes; and continually adjusting the target glucose level signal based on a calculated longer term trend represented by at least values of the measured glucose level signal over the longer term, wherein continually adjusting the target glucose level signal is based on a function of measured glucose levels over a recent period, the function is a weighted sum computed using a scaling factor with which measured glucose levels are multiplied to determine offsets caused on the target glucose level signal by respective contributions from measured glucose levels, wherein the scaling factor varies depending on the respective measured glucose levels, wherein the scaling factor is a relatively low value for high values of measured glucose level and progressively higher for lower values of measured glucose level.