Arbor Day (from the Latin arbor, meaning tree) is a holiday in which individuals and groups are encouraged to plant and care for trees. It originated in Nebraska City, Nebraska, United States during 1872 by J. Sterling Morton. The first Arbor Day was held on April 10, 1872, and an estimated 1 million trees were planted that day.

Many countries now observe a similar holiday. Though usually observed in the spring, the date varies, depending on climate and suitable planting season.