Geocaching is a type of global treasure hunt of people looking for caches, or hidden stashes of objects. Geocaching may also be described as a series of hide-and-seek games, where hiders provide online clues for seekers. Seekers use global positioning system (GPS) devices to find hidden caches.

Caches are the hidden treasure. After registering online, geocachers look for coordinates (the longitude and latitude) of caches. Caches have two or three parts: a waterproof container, a logbook to list the people who visit the cache, and sometimes a low-cost trinket or geocoin. (Geocoins are metal medallions made by individual geocachers or organizations. Like other cache items, geocoins are not worth much money.) Common materials found inside caches might include foreign currency, keychains, ornaments, or booklets. Valuable objects, food, or other items that could be easily damaged are not allowed in geocaching.

Although caches can be hidden (as false rocks or behind real ones), they are not buried. Latitude and longitude provide the caches location. Geocachers also give clues online. For example, a cache may be hidden on one side of a tree, or may only be visible from a certain angle. Because geocachers want the hobby to remain safe for people of all ages, caches are located 150 feet from railroad tracks.

Some caches are drive-up (also called cache and dash), but most require a good walk. For this reason, geocachers are advised to bring a map, a GPS device, an extra set of clean clothes, and an umbrella.

Since geocaching is generally an outdoor activity, the participants are required to know their environment. Travelers sometimes get to know an area they are visiting by trekking to find caches, while weekend geocachers notice features in their own habitat.

Geocaching is a way to learn about the environment and help clean it up. Cache in, trash out is a common activity. Earthcaches (developed by the Geological Society of America) provide educational lessons about the physical geography of the caches region.

The hobby has changed a little since its start in Oregon in 2000, when it was called geostashing. Geocaching was started by a group of people who were interested in technology and geography. They used GPS devices and the Internet to re-invent the older hobby of letterboxing. Letterboxing is a lot like geocaching, but the clues are provided in booklets or other printed material.

As geocaching has grown, virtual caches, or caches that don't involve an actual physical object, are no longer allowed. Most of the time, these virtual caches involved getting geocachers to a historical site or scenic vista. Waymarking is similar to virtual geocaching. Waymarking clues lead participants to interesting spots or trails. Some national parks and wilderness areas do not allow geocaching, although they encourage waymarking as a good way to see the area.

Many state and local parks organize or participate in their own geocaching events. Some may be tied to historical or seasonal events (a Mardi Gras geocache in New Orleans, Louisiana, for example) or may focus on local environmental opportunities (a canoe-in event in Minnesota.)

Geocaching has evolved from a small hobby to huge, well-organized treasure hunts for people of every age and ability. There are nonprofit organizations, as well as businesses for geocaching. The largest is geocaching.com.