The monograph belongs to the Series in Operations Research, and presents the method and methodology of Analytic Hierarchy Process (AHP) - one of the most popular tools of the practical multiple-criteria decision making (MCDM). Additionally, the least squares and its modifications in the weighted least-square methods, weighted least worst squares method, weighted least absolute error method, logarithmic least-square method reducing to GMM solution, simple column sum and simple-scaled column sum methods, a cosine maximization method, and some others are described and compared by the so-called minimum violations criterion and conformity criterion. [Extracted from the article]