Harmonic emissions of variable speed wind turbines (WTs) are a well-known issue, but little information that is based on field measurements on actual machines has been published on the subject. In this paper, the harmonic behavior of modern WTs using extensive measurements performed on commercially available machines is discussed. Specific issues addressed include the shape and the frequency range of the harmonic current spectrum, the variation of the harmonics with the WT operating point, the statistical characteristics of their magnitude and phase angle, the effect of grouping and time-averaging, as well as their symmetrical component characteristics. The objective of the paper is to outline important general characteristics of the harmonic behavior of WTs, rather than to analyze specific machines or compare alternative WT designs