Contains The History, A Treatise on the Manners of the Germans, The Life of Gnaeus Julius Agricola, and A Dialogue Concerning Oratory, or the Causes of Corrupt Eloquence.
About the books (from Wikipedia):
In an early chapter of the Agricola, Tacitus asserts that he wishes to speak about the years of Domitian, Nerva, and Trajan. In the Histories the scope has changed; Tacitus says that he will deal with the age of Nerva and Trajan at a later time. Instead, he will cover the period from the civil wars of the Year of Four Emperors and end with the despotism of the Flavians. Only the first four books and twenty-six chapters of the fifth book survive, covering the year 69 and the first part of 70. The work is believed to have continued up to the death of Domitian on September 18, 96. The fifth book contains—as a prelude to the account of Titus’s suppression of the Great Jewish Revolt—a short ethnographic survey of the ancient Jews, and it is an invaluable record of Roman attitudes towards them.
The Germania (Latin title: De Origine et situ Germanorum) is an ethnographic work on the Germanic tribes outside the Roman Empire. The Germania fits within a classical ethnographic tradition which includes authors such as Herodotus and Julius Caesar. The book begins (chapters 1–27) with a description of the lands, laws, and customs of the various tribes. Later chapters focus on descriptions of particular tribes, beginning with those who lived closest to the Roman empire, and ending with a description of those who lived on the shores of the Baltic Sea, such as the Fenni. Tacitus had written a similar, albeit shorter, piece in his Agricola (chapters 10–13).
The Agricola (written ca. 98) recounts the life of Gnaeus Julius Agricola, an eminent Roman general and Tacitus’ father-in-law; it also covers, briefly, the geography and ethnography of ancient Britain. As in the Germania, Tacitus favorably contrasts the liberty of the native Britons with the tyranny and corruption of the Empire; the book also contains eloquent polemics against the greed of Rome, one of which, that Tacitus claims is from a speech by Calgacus, ends by asserting that Auferre trucidare rapere falsis nominibus imperium, atque ubi solitudinem faciunt, pacem appellant. (To ravage, to slaughter, to usurp under false titles, they call empire; and where they make a desert, they call it peace. — Oxford Revised Translation).
There is uncertainty about when Tacitus wrote Dialogus de oratoribus. Many characteristics set it apart from the other works of Tacitus, so that its authenticity has been questioned. In style it seems closer to Cicero; it lacks for example the incongruities that are typical of his historical works. It may however be an early work. It is dedicated to Fabius Iustus, a consul in AD 102. Its style may be explained by the fact it deals with rhetoric. In Latin rhetoric the structure, language, and the style of Cicero was the usual model.
About Tacitus (from Wikipedia):
Publius (or Gaius) Cornelius Tacitus (AD 56 – AD 117) was a senator and a historian of the Roman Empire. The surviving portions of his two major works—the Annals and the Histories—examine the reigns of the Roman Emperors Tiberius, Claudius, Nero and those who reigned in the Year of the Four Emperors. These two works span the history of the Roman Empire from the death of Augustus in AD 14 to (presumably) the death of emperor Domitian in AD 96.