A missionary is a person who travels to another place to share his or her religious beliefs with others. Missionaries often combine proselytizing (sharing their faith) with other acts of service, such as through social justice, economic development, education, and/or health care.

A missionary can be a part of any religious faith, including Christianity, Buddhism, Hinduism, Sikhism, and Islam. The exception to this is Judaism, as most modern Jews believe it is more important to encourage Jews to remain faithful in following Jewish laws and traditions than it is to invite new followers.

Throughout the Age of Exploration (15th century to 19th century CE), several explorers were motivated by a desire to spread their religious beliefs to the indigenous people of the lands they encountered. Dr. David Livingstone was one such explorer whose travels through continental Africa were driven by his personal motto: “Christianity, Commerce, and Civilization.” Livingstone believed that sharing his Christian faith with the people groups of Africa would ultimately create greater opportunities for trade networks, eliminating the need for slave labor, which would then promote a more prosperous continent.