Chapter 3 is devoted to the bifurcation theory of semilinear Robin problems. Especially, we present a brief description of basic definitions and results about the theory of positive mappings in ordered Banach spaces essentially due to Kreı̆n–Rutman (1962) and the local static bifurcation theory from a simple eigenvalue due to Crandall–Rabinowitz (1971), which form a nonlinear functional analytic background in the sequel.