A missionary is someone who travels to another place to share their religious beliefs and help people. Christian missionaries, for example, go to different countries or regions to teach about Christianity, often building churches, schools, and hospitals along the way.

Throughout history, missionaries have played complex roles. Some brought education and medical care to remote areas where these services didn't exist. Catholic missionaries in California during the 1700s established missions that taught farming and crafts, though they also forced Native Americans to abandon their own cultures. Protestant missionaries in Africa and Asia during the 1800s opened schools and translated the Bible into local languages, helping preserve some languages that might have been lost.

While missionaries are most often associated with Christianity, other religions have missionaries too. Buddhist missionaries spread Buddhism from India across Asia centuries ago.

Today, missionaries continue working worldwide. Some focus purely on religious teaching, while others combine faith with practical help like building wells, teaching literacy, or providing medical care. The word can also be used more broadly: someone might joke about a friend being a “missionary” for a cause they're passionate about, like vegetarianism or recycling, meaning they enthusiastically try to persuade others to think the same way.