Marginal costing is a technique that differentiates between fixed and variable costs. It treats variable costs as product costs and fixed costs as period costs. Under marginal costing, only variable costs are considered in inventory valuation. Absorption costing treats both fixed and variable costs as product costs and includes a share of fixed costs in inventory valuation. The chapter provides definitions and concepts related to marginal costing, characteristics that distinguish it from absorption costing, and how profit is calculated differently under each method.