Via very simple models, this chapter introduces to the basic structure of the marginal/neoclassical approach to competitive value and income distribution, explaining the direct and the indirect factor substitution mechanisms that allow the derivation of decreasing demand curves for the factors labour, land and capital (assumed in this chapter to consist of a single good). For the newcomer to economics, the notions of production function, isoquant, isocost, cost minimization, utility function, marginal utility, indifference curve, utility maximization are synthetically introduced, postponing more rigorous definitions and special cases to Chaps. 4 and 5. The First Fundamental Theorem of Welfare Economics is presented in intuitive terms for an exchange economy and for a two-factors production economy; to this end Pareto efficiency, the Edgeworth box and the Production Possibility Frontier are introduced. No more advanced mathematics is used than simple partial derivatives and the rule for the derivative of implicit functions. Robinson Crusoe is used to show that according to this approach the market solves efficiency issues in the same way as an optimally planned economy. The chapter ends by contrasting marginal/neoclassical and classical approach on labour exploitation, relative wages, Say’s Law. The root of the differences is found in the presence in the marginal approach of factor substitution mechanisms derived from a generalization of Ricardian intensive rent theory. The online Appendix to the chapter contains additions on the stationary state assumption and on the determination of intensive rent when advanced wages are separated from seed-corn.