Certain gems have traditionally been associated with different months of the year, and are thought lucky or important for people born under their "influence". This probably stems from ancient belief that gems came from the heavens. The most popular selection today is shown below.

Many cultures associate gems with the signs of zodiac, and others with the months of the year, but the selection varies from country to country, perhaps influenced by availability of gems, local traditions, or fashions. The custom of wearing birthstone jewellery started in 18th – century Poland, and has since spread throughout the world.