The preceding chapters have been concerned with the spectrum analysis of sinusoids and noise at a particular point in time (or a single spectrum for all time). This chapter introduces the Short-Time Fourier Transform (STFT)--a time-ordered sequence of spectral estimates, each using a finite-length analysis window. The STFT is used to compute the classic spectrogram, used extensively for speech and audio signals in general [132,57,199,162,226,74,81]. Finally, we point to methods for making spectrograms correspond better to audio perception, so that what you see is what you hear, to a greater extent. In particular, a loudness spectrogram based on a psychoacoustic model of time-varying loudness perception is described.