This chapter introduces statistical approaches for quantifying the variability and precision of measurements. The chapter starts by introducing the most common indices of dispersion for quantifying the variability, followed by defining basic concepts such as accuracy, precision, and resolution of measurements, as well as the distinction between systematic and random measurement errors. A model of random errors is introduced and used to derive confidence intervals for estimating the mean of a measured quantity of interest based on a sample of measurements. Finally, statistical tests for comparing alternatives based on measurements are introduced. The cases of paired and unpaired observations are covered separately.