Wellbore temperature sensing apparatus for use in sensing temperature along a wellbore, comprising: tubing being metallic tubing, comprising a plurality of temperature sensor modules (120a, 120b, 120c ... 120n) provided at locations along the inside of the tubing , having electrical properties that vary with temperature; and an electrical network comprising a plurality of wires and said plurality of temperature sensor modules, wherein the plurality of wires and plurality of temperature sensor modules are configured as a matrix by which the plurality of wires comprises a first group of wires and a second, different group of wires and each wire of the first group is electrically connected to each wire of the second group once, each electrical connection being by a respective temperature sensor module of the plurality of temperature sensor modules (120a, 120b, 120c ... 120n), such that each temperature sensor module can be individually electrically connected by a pair of wires comprising a first wire from the first group and a second wire from the second group ; a wireless data communication module coupled, wirelessly, by a separate wireless connection or electrically by a wired connection, to the apparatus , and arranged to, in use, wirelessly transmit along the well, signals indicative of a temperature sensed in the wellbore by the apparatus ; wherein the wireless data communication module is configured to transmit said signals acoustically and/or electromagnetically, and a power source configured to provide operational power to the apparatus ; wherein the power source is arranged to be provided as an in-well power source in use tubing being metallic tubing, comprising a plurality of temperature sensor modules (120a, 120b, 120c ... 120n) provided at locations along the inside of the tubing , having electrical properties that vary with temperature; and an electrical network comprising a plurality of wires and said plurality of temperature sensor modules, wherein the plurality of wires and plurality of temperature sensor modules are configured as a matrix by which the plurality of wires comprises a first group of wires and a second, different group of wires and each wire of the first group is electrically connected to each wire of the second group once, each electrical connection being by a respective temperature sensor module of the plurality of temperature sensor modules (120a, 120b, 120c ... 120n), such that each temperature sensor module can be individually electrically connected by a pair of wires comprising a first wire from the first group and a second wire from the second group ; a wireless data communication module coupled, wirelessly, by a separate wireless connection or electrically by a wired connection, to the apparatus , and arranged to, in use, wirelessly transmit along the well, signals indicative of a temperature sensed in the wellbore by the apparatus ; wherein the wireless data communication module is configured to transmit said signals acoustically and/or electromagnetically, and a power source configured to provide operational power to the apparatus ; wherein the power source is arranged to be provided as an in-well power source in use <EOS>