This document discusses threshold cointegration models for analyzing credit spread dynamics between corporate bond yields and government bond yields. It presents three main threshold cointegration models - the Lo-Zivot model, the Hansen-Seo model, and the Enders-Siklos model - and applies them to study the relationships between various credit spreads (Moody's Aaa bond index, Baa bond index) and government bond rates (10-year Treasury, 20-year Treasury Ibbotson index). The results provide evidence of asymmetric adjustment and nonlinear dynamics in the credit spread relationships. Out-of-sample forecast evaluations show that threshold cointegration models generally outperform traditional linear cointegration models in forecasting credit spreads.