The discussion paper for the September issue of Bayesian Analysis will be the paper “Using Stacking to Average Bayesian Predictive Distributions by Yuling Yao, Aki Vehtari, Daniel Simpson, and Andrew Gelman. It is available from as advanced publication. We invited Men Li, Peter Grunwald and Bertrand Clarke to discuss the paper. We welcome contributions to the discussion. These should be no more than two pages in length, using the BA latex style. They should be submitted to the journal using the EJMS system, before June 15, 2018.