Pedigree and performance data (production and reproduction records) recorded on divergent single-trait selection lines conducted for sheep genetics research during the 1950s to the 1990s. The original lines of Merino sheep were divergently selected on clean fleece weight, crimp frequency, weaning weights and skin wrinkle, and included a control line. Other lines that were established later were selected on a combination of performances in fertility and clean fleece weight, and in fleece rot and body strike. The lines were used to: estimate genetic parameters, demonstrate direct and correlated responses to selection, understand the physiological and biological mechanisms underlying the selection responses and identify the importance of genotype X environment interactions.