This is a new book in the Osprey Men at Arms series by Andrei Pogacias on the ancient Dacians and Getae. This isn't the first Osprey treatment of the Dacians. They did a series back in 1982 on Rome's enemies, and the Dacians were lumped in with the Germanic tribes. There has been a fair amount of archaeology and other academic work since then, although we still don't know much, and what we know comes from Greek and Roman sources.
This author discusses our sources and describes the Getae as primarily residing in the lowlands around the Danube in what is modern Romania, spreading towards the Black Sea. The Dacians are mainly further inland in the Transylvania mountains, looking more to the west. These are not neat geographical lines; both peoples intermingled.
We then get chapters on the social structure and the armies. The Getae appear to have been chiefly mounted, while the Dacian armies had a more balanced infantry and cavalry army. Numbers in ancient sources are notoriously unreliable, but Dacia may have had a population as large as one million. Both used fortifications, and there is decent archaeological evidence for the Dacian forts.
There is a chapter on campaigns, which starts with the less well-known early wars against the Persians and then the Macedonians. The Getae were allies of Mithridates the Great in his wars against the Romans. The story of battles against the Romans is well known, starting with early victories against Domitian and then defeats in Trajan's wars. Sources are more robust for these campaigns, including the famous Trajan's Column in Rome.
Finally, a chapter on weapons and equipment. This includes the sica and falx archaeological finds, most closely associated with the Dacians. This is also reflected in the colour plates. The author is a reenactor who brings that experience to the story. Overall, a handy introduction.
If you want to start a new ancient army, you could do worse than the Dacians. With Sarmatian allies, they are more balanced than many tribal armies, and Warlord does some lovely infantry in 28mm, although there are not enough falx in the box for me.