The first stage of the challenge (Stage 1a) consisted of 20 ligands for pose prediction (Fig. ) and 154 compounds for affinity ranking of which a subset of 34 ligands was included in the binding free energy calculations. For this stage, the organizers only provided a FASTA sequence for the protein BACE-1 and SMILES strings for the different compounds. Participants were free to use any of the available crystal structures. After this stage, 20 holo crystal structures of BACE-1 from the pose prediction dataset (without the ligands) were released for Stage 1b. Participants had the option of taking advantage of the released BACE-1 receptor structures and resubmitting their binding pose prediction for the same 20 ligands. In Stage 2, complete co-crystal structures of the 20 ligands were made available to test whether this additional knowledge about protein-ligand interactions could improve the affinity rankings and the binding free energies predictions.