This document explains the factors influencing the yields of debt securities, outlining how characteristics such as credit risk, liquidity, tax status, and term to maturity affect investor decisions and yield estimation. It discusses the importance of credit ratings and the role of rating agencies in assessing credit risk, as well as the differences between before-tax and after-tax yields. Additionally, it describes how yield differentials, particularly during varying economic conditions, impact the attractiveness of different types of bonds to investors.