Probably one of the most iconic names in beauty products - Avon began producing costume jewelry in 1963 and continues to do so today. The company was founded in 1886, focusing mainly on perfumes. It was founded by David McConnell and offered, at the time, an unheard of opportunity for women to go into business for themselves. In the late 1800s if women worked, it was mainly in factories, as housekeepers or maids and as laborers on farms. The opportunity to sell perfume opened doors for women in a supportive way.
The company, originally known as the California Perfume Company, grew quickly, growing to 5,000 representatives by 1900. In the 1929 CPC began using the word Avon for some of their products and in 1932 received their first trademark approval. In 1939 the company officially became Avon Products, Inc. and began offering more products such as skin care lines.
It wasn't until 1963 that Avon began offering jewelry to customers, but it wasn't for sale, the jewelry was offered as a gift with purchase. The jewelry became popular among Avon's client and a demand began building for the jewelry as a separate purchase from the perfume and skin care products.
Avon began experimentally selling a few pieces in 1965, but until 1970 most pieces were only available with an Avon product. After 1970 the pieces became more and more popular and the costume jewelry became it's own section of products available in the Avon catalog.
For vintage collectors this timeline can be a helpful tool - odds are most of the pieces you'll find are going to be from the 70s or newer. Most Avon jewelry is decent quality - but not very high-end. So you'll need to look for pricing accordingly. Some of the most popular pieces were perfume pendants. These were very big in the 70s, usually very heavy and well made, more so at least than some of the later vintage costume jewelry pieces.
All Avon pieces will be marked. They've always done a great job of branding their items and it's pretty consistent. The main way you'll be able to date items is based on the design of the piece. 60s and 70s pieces will have a lot of plastic - lucite and thermosets mainly. Look for older pieces to be made of metal in goldtone color and real rhinestones. Also look for resin cameo pieces - Avon created a lot of those!
I've posted some pictures of different Avon pieces I've had or sold for reference. Happy hunting!