The Fifth Assessment Report of the Intergovernmental Panel on Climate Change concluded that warming of the climate system since the start of the instrumental record was unequivocal. While this conclusion does not solely rest upon the surface temperature record, this record is a key aspect underpinning this finding. Herein is discussed the observational evidence basis for increases in global surface temperatures since the start of the instrumental record. This chapter starts by discussing how the measurements have been taken over time. It is then described how necessary efforts to adjust the records to account for time-varying biases have been performed. Resulting global estimates and efforts at quantifying uncertainties therein are then discussed. Changes in temperature extremes are briefly highlighted. This chapter closes with a view to future research directions and innovations.