This document discusses performing a three-way join of relations R, S, and T in a single MapReduce job. It presents two algorithms for performing the join: a nested loop join and a sort-based join. It also discusses how to determine the number of reducers to use, giving an example where using a non-square matrix of reducers can lead to data replication or reducer inefficiency. Experimental results show the three-way join took 37 seconds to complete.