GEM, written with all capital letters, may refer to:

• GEM (girl group), a Japanese idol pop group formed by Avex Trax
• G.E.M. (singer), a pop singer from Hong Kong
• GEM (album), a 2007 album by Beni Arashiro
• G.E.M. (album), a 2008 album by G.E.M.

GemStone may refer to:

• Gemstone, a type of mineral
• GemStone IV (or GemStone III), an online multiplayer game by Simutronics Corporation
• GemStone Systems, a data management company
• Gemstone (database), an object-oriented database

A gemstone or gem (also called a fine gem, jewel, or a precious or semi-precious stone) is a piece of mineral crystal, which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli) or organic materials that are not minerals (such as amber or jet), are also used for jewelry, and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone. Apart from jewelry, from earliest antiquity engraved gems and hardstone carvings, such as cups, were major luxury art forms. A gem maker is called a lapidary or gemcutter; a diamond worker is a diamantaire.

RubyGems is a package manager for the Ruby programming language that provides a standard format for distributing Ruby programs and libraries (in a self-contained format called a "gem"), a tool designed to easily manage the installation of gems, and a server for distributing them. RubyGems was created around November 2003 and is now part of the standard library from Ruby version 1.9.