Ratios and proportions are foundational to student understanding across multiple topics in mathematics such as slope, constant rate of change, and similar figures, which are all fundamental to algebraic concepts and skills. The CCSS-M includes concepts and skills that support students’ understanding of ratios and proportions. Often times students struggle with ratios and proportional reasoning because of misconceptions, which were established in earlier grades. Mathematical misconceptions are faulty and incorrect ideas resulting from students’ misunderstanding about a mathematical idea or concept. This article describes misconceptions that impede successful learning with ratios and proportional reasoning and provides examples of lesson components for teaching ratios and proportions.