The Senatus Consultum de Cn. Pisone Patre is a senatorial decree issued in AD 20 following the trial of Gnaeus Calpurnius Piso, the governor of Syria, who was accused of rebellion against Tiberius following the death of his heir Germanicus. It survives on several inscriptions and is among the most important documents from the early Principate. This new edition, with translation and commentary, sets the text within its contemporary context, considering it alongside other texts (including Tacitus' Annales), coins, and monuments, focusing upon the development of Tiberian political discourse. It explores how contemporary observers (including Valerius Maximus and Velleius Paterculus) understood and contributed to the shaping of dynastic rule at Rome after the death of Augustus in AD 14. It analyses how the Principate continued to evolve under his successor Tiberius, and explores the role of different individuals and groups in negotiating these political changes.