This document discusses factors that influence earnings, including human capital, education as a signal, compensating differentials, and discrimination. It provides examples of earnings differentials between graduates from top vs. lower ranked universities based on signaling theory and between high vs. low GPA graduates based on human capital theory. The document also examines earnings differences between more vs. less attractive individuals, hazardous waste vs. produce truckers, and the world's best writer vs. physical therapist based on productivity and compensation for risk. Charts show changes over time in the female-to-male wage ratio by occupation and factors explaining the gender wage gap.