The volume contains original articles and survey papers on approximation theory (e.g. approximation by polynomial and rational functions, approximation by operators, orthogonal polynomials, meromorphic functions), optimization (e.g. integer, nonlinear, quadratic, multi-objective, fractional, semi-infinite), control theory (e.g. singular control problems), equations and inequalities (e.g. complexity), mathematical economy (e.g. core theory, infinite horizon economics), and shows the relations among these topics.