ISO 4259-1:2017 specifies the methodology for the design of an Interlaboratory Study (ILS) and calculation of precision estimates of a test method specified by the study. In particular, it defines the relevant statistical terms (Clause 3), the procedures to be adopted in the planning of ILS to determine the precision of a test method (Clause 4), and the method of calculating the precision from the results of such a study (Clauses 5 and 6). The procedures in ISO 4259-1:2017 have been designed specifically for petroleum and petroleum related products, which are normally considered as homogeneous. However, the procedures described in ISO 4259-1:2017 can also be applied to other types of homogeneous products. Careful investigations are necessary before applying ISO 4259-1:2017 to products for which the assumption of homogeneity can be questioned.