Gem

Gems are the "exchange" currency between "real life" money and Heroes of the Storm.

Earning gems

 * Purchased directly from the Gem Shop with real life money.
 * Reaching account-level milestones: Every 25 Player levels you are rewarded with.

Uses
Gems can be used to purchase:
 * Heroes
 * Skins
 * Mounts
 * Boosts
 * featured items (such as Bundles).

Trivia

 * In the Technical Alpha, Gems were a type of Artifact that could be equipped to to a player's Artifact Slots.