No one knows when or how the Panchatantra was composed. However, according to the legend, a Brahmin scholar named Vishnu Sharma designed it to teach the sons of a king something about life, neeti (policy) and real-politik. The result was a mosaic of interlocking stories that emerge from one another, and leave you with a lot of understanding about dealing with life.
The book reached Arabia sometimes in the fifth century AD, and then later it reached Europe, where it is believed to have led to development of Aesop's fables. It is difficult to judge how it has affected these societies, but in India it has had tremendous impact, which continues to this day. Its lessons are alive and well even today, and almost every child will know at least one story from Panchatantra.
The present translation from the original Sanskrit is an excellent one, and tries to be as faithful to the original as possible. However, Sanskrit and English are two very different languages in their orientation (though they belong to the same family). As a result, the translation of many ideas suffers. Also, some of the particularly interesting comments have been left out altogether. So if you know Hindi or Sanskrit, then you should try and buy the Panchatantram in Sanskrit/ Hindi (published by Motilal Banarasi Das of Delhi).
Even so, going through this book may open up another world for you, particularly if you were not brought up in India. It will change your perspective on many ordinary things and challenges that you face in everyday life. There are stories which teach you how to recognise deceit, fraud, cheating, make friends, cooperate with people, and generally get on with life. And there are arguments over particular positions that the protagonist takes, so that you get to see both points of view. You would also find this book particularly useful if you are dealing with Indians in business or in diplomacy, just as Western audiences have found the Art of War (Sun Tzu) to be a fascinating insight into the Chinese mind.
As the stories are built around animals, many people mistake these for nursery stories or for fables. This is not correct. Panchatantra is as relevant for adults as it is for teenagers. In fact some of the stories involving adults are not appropriate for young children (<13 years).
All in all, an excellent book for your own enjoyment or as a gift to a young or old friend.