There were a total of 19 Great Rings made by the Elves of Eregion during the Second Age. Most of these Great Rings were made with the help of Sauron. Three were gifted to the Elves, Nine were given to the Race of Men, and Seven were given to the Dwarves. One other was made by Sauron alone, in secret, and was kept by him until it was cut from his finger after the Last Alliance of Elves and Men.

The Elven-smiths of Eregion made many rings during the middle years of the Second Age but only the aforementioned 19 and the One Ring are considered "Great".

All of the Great Rings shared two powers, while each Ring also had its own power particular to the Ring and its bearer. The two powers which were native to all of the Rings were as follows:

The Great Rings would lengthen the lives of those who bore them, allowing them to not age. The Elves, being already immortal, were not effected by this, but any Mortal bearer would have their life "stretched". This can be seen in the unusually long lives of both Bilbo and Gollum.

The other power of all of the Great Rings was their ability to make the wearer invisible. All of the Great Rings had this power, though it seemed that it did not effect the Elves. This may be explained by the fact that Sauron had no hand in the making of, nor had he ever touched, the Three Elven Rings.

The invisibility was at first temporary but as in the case of the Nazg├╗l, the bearer could become permanently invisible because they were drawn into the Wraith-world.

There are strong hints in the texts that the Dwarves were strangley resistant to the effects of the Great Rings and though surely they used them, there is little evidence of it.
Encyclopedia entry originally written by Nienna-of-the-Valar