Immunohistochemical diagnostic testing for programmed cell death-ligand 1 (PD-L1) has been approved for targeted treatment of several major cancer types including non-small cell lung cancer, NSCLC. However, the semi-quantitative scoring of PD-L1 expression is complex and requires training of pathologists to reduce inter- and intra-reader variability. Here we present some of our data for a worldwide, expert-led training in PD-L1 interpretation and scoring of NSCLC cases, conducted over a two-year period, 2016-2017, using glass slides or equivalent digital images.