This essay consists of two parts. Part one, which comprises four sections, is written for a general readership and explains the background to the Global Collaboratory on the History of Labour Relations, 1500-2000. It elaborates on the key social and economic issues it wants to address (including social inequality) and on how the data collected by the Collaboratory can be combined with other socio-economic macro and micro data for this purpose. The essay shows furthermore how the project stands in the context of a long tradition of categorising labour and labour relations, and how the taxonomy developed by the project to categorise labour relations worldwide for at least the past five hundred years is constructed. As the project is work in progress, the taxonomy is updated when new datasets and insights become available. Part two is written specifically for members of the Collaboratory and other taxonomy users, and explains what modifications were made to the taxonomy, and why. The Appendix gives an overview of the definitions of labour relations as used in the taxonomy.