This chapter is about measuring voltage and current waveforms as well as power quality. Waveform sensors can show the wave shape of voltage and current; as opposed to only their RMS values, or only the phasor representation of their fundamental components. We discuss event-triggered waveform capture, and also measuring distortions in voltage and current waves, including harmonics, inter-harmonics, and notching. We cover event detection, event capture, and statistical analysis of events in waveform measurements, event signature evaluation, event classification, and pattern recognition. Another important subject in this chapter is the analysis of faults and incipient faults. This includes the analysis of fault signatures, faults in underground power cables, overhead power lines, transformers, capacitor banks, and distributed energy resources. We also discuss harmonic synchrophasors and their applications in harmonic state estimation and topology identification. Synchronized waveform measurements, waveform measurement units, synchro-waveforms, and their applications are also covered. Finally, we discuss accuracy in waveform measurements, and the impact of noise and interference.