The history of Guam starts with the early arrival around 2000 BC of Austronesian people known today as the Chamorro Peoples. The Chamorus then developed a "pre-contact" society, that was colonized by the Spanish in the 17th century. The present American rule of the island began with the 1898 Spanish–American War. Guam's history of colonialism is the longest among the Pacific islands.

The Chamorro people are the Indigenous people of the Mariana Islands, politically divided between the United States territory of Guam and the encompassing Commonwealth of the Northern Mariana Islands in Micronesia, a commonwealth of the US. Today, significant Chamorro populations also exist in several U.S. states, including Hawaii, California, Washington, Texas, Tennessee, Oregon, and Nevada, all of which together are designated as Pacific Islander Americans according to the U.S. Census. According to the 2000 Census, about 64,590 people of Chamorro ancestry live in Guam and another 19,000 live in the Northern Marianas.