Annals by Tacitus is a collection of historical accounts written during the the reigns of Tiberius, Claudius, Nero. Tacitus also chronicled the events during the Year of the Four Emperors, which included Galba, Otho, Vitellius, and Vespasian, in that order.

While the overall theme of the work is the political history of the Roman Empire during Tacitus's time, there is an emphasis on the brutality of politics, war, and tyranny. In this regard, a sub-theme of the book is political commentary with a focus on the nature of morality.

In fact, the descriptions of Machiavellian politics and the atrocities of war in this book were so vivid that critics of Tacitus during his time claimed his works were exaggerated. Another theme of the of the work is Tacitus's opinion that the Roman Empire began to decline under Tiberius's rule. Tacitus based this opinion on the increasing brutality and deceit found in Roman political life, in which emperors, senators, and military officials formed secret alliances to eradicate each other. This climate of fear, greed, paranoia, and violence contributed to the gradual erosion of the Roman Empire's power.

The writings of Tacitus also have a subtle existential theme, or point of view, in that he believed that the suffering of the Roman people is eased by suffering together.