The Roman Empire spread way beyond Italy in ancient times. The territories under their control were allowed to keep their culture and their Greek language. They were also allowed to issue coins locally. These coins had Greek inscriptions on them, a lot of the times and include a myriad of reverses that were important to the local people living in the area. 
The standard reference work on these coins is Greek Imperial Coins And Their Values by David R. Sear. This work is a great bird's eye view of many Greek Imperial or otherwise known as Roman Provincial coins. Every emperor is included there, including some cultures that were present during the times of the Roman empire. Additional references are given to coins that were quasi-autonomous, or in other words, struck without the portrait of the emperor. Some of them are interesting and feature the portrait of the Roman Senate and Roma. 
Overall, this is an interesting subject to learn about, explore and to collect. The advantage is that you can have reverse designs that you would not have on the Roman Imperial coins themselves, which featured strictly Roman motifs most of the time. Also to note, that some emperors, which are at times referred to as usurpers only issued coins in the province or city under their control. So you can only have a Roman provincial coin of them. Another benefit of Roman provincial coins is that they feature portraits of the imperial family which are otherwise not present on Roman Imperial coins. So, in conclusion, Greek Imperial or Roman Provincial coins made an amazing addition and make any ancient Roman coin collection more complete and more fascinating. 
You can find a selection of over 1000 Roman provincial ancient coins not listed here. Seeing them is very simple by clicking here to go to my store, and then scrolling down to the appropriate Ancient ROMAN PROVINCIAL Coins  category. There is more than one so it is great to check both out. You can also get more familiar with how to use my store by clicking here.

An Overview of Different Ancient Roman Provincial / Greek Imperial Coins

This section features a selection of 27 different ancient coin types that are covered in my video above. You can learn a lot more about them by exploring my eBay store. I just picked out some of the nicest quality, and some of the rarest Roman provincial coins that I have. One of them even being a type that I believe may be a unique or unpublished example. You can learn a lot from the coins given below. Enjoy.