This chapter contains sections titled: Introduction An Overview of Nonstationary Behavior and Time–Frequency Analysis Theoretical Background on Nonstationarity High‐Resolution Multi‐taper Spectrograms Spectrum Analysis of Radar Signals Discussion References Introduction An Overview of Nonstationary Behavior and Time–Frequency Analysis Theoretical Background on Nonstationarity High‐Resolution Multi‐taper Spectrograms Spectrum Analysis of Radar Signals Discussion References