This chapter discusses paired comparisons, presents signal detection theory and provides gives references to the software R-packages used. There are a number of procedures to analyze data obtained in the paired comparisons response format. The chapter mentions the following: Thurstone’s model, Bradley-Terry’s model and Scheffé’s approach. Both the Thurstone model and the Bradley-Terry model are called probabilistic or stochastic models. The chapter illustrates the analysis of paired samples on the basis of the Bradley-Terry model, as the available programs for this model are flexible and have many options. Residuals in modelling of paired comparisons may be – among others – the result of violations of the transitivity axiom, on which designs with paired comparisons are based.