Introduction to the Stability of Time-Delay Systems -- Introduction to Analytic Curves -- Analytic Curve Perspective for Time-Delay Systems -- Computing Puiseux Series for a Critical Pair -- Invariance Property: A Unique Idea for Complete Stability Analysis -- Invariance Property for Critical Imaginary Roots (CIRs) with Index g = 1 -- Invariance Property for Critical Imaginary Roots with Index n = 1 -- Invariance Conjecture and Frequency-Sweeping Framework -- Complex Stability for Time-Delay Systems: A Unified Approach -- Extension to Neutral Time-Delay Systems -- Concluding Remarks and Further Perspectives.