Reviews the sources and effects of power frequency conducted harmonic current emissions in the frequency range up to 2 kHz on the public electricity supply, and gives an account of the reasoning and calculations leading to the existing emission limits for equipment in the editions of IEC 61000-3-2, up to and including the second edition (2000) and its first amendment (2001), and in the first edition of IEC 61000-3-12 (2004).