A Practice Note explaining how to determine whether a transaction is reportable under the Hart-Scott-Rodino Act. This Note sets out the HSR thresholds and explains how to determine whether a transaction meets the size-of-person and size-of-transaction tests. It also offers guidance on determining the filing parties' ultimate parent entities (UPEs), applying aggregation principles under the HSR rules, and describes certain potentially reportable transactions that may be easily overlooked, such as back-end and secondary acquisitions.