From the beginning Chanel No. 5 has always been exclusive. It was first released in 1921 as a Christmas gift to Mlle.'s best customers and was limited to only 100 flacons. When these customers started coming back, asking for more, it was officially launched as "Chanel Nº 5" in 1922. Word is that this scent was the No. 5 bottle out of 10 samples presented to her, and that when asked how she would name it, she replied, "I always launch my collection on the 5th day of the 5th month, so the number 5 seems to bring me luck – therefore, I will name it Nº 5."
Here's an excerpt from a great history of Chanel's most famous fragrance we found on OnSugar blog Older Girl Beauty. Check it out: