Ash Wednesday is a holy day of prayer and fasting in many Western Christian denominations. It is preceded by Shrove Tuesday and marks the first day of Lent, the six weeks of penitence before Easter.

Ash Wednesday is observed by Catholics, Lutherans, Moravians, Anglicans, Methodists, Nazarenes, as well as by some churches in the Reformed tradition, including certain Congregationalist, Continental Reformed, and Presbyterian churches.

Ash Wednesday is traditionally observed with fasting and abstinence from meat in a number of Christian denominations. As it is the first day of Lent, many Christians begin Ash Wednesday by marking a Lenten calendar, praying a Lenten daily devotional, and making a Lenten sacrifice that they will not partake of until the arrival of Eastertide.

Many Christians attend special Ash Wednesday church services, at which churchgoers receive ash on their foreheads. Ash Wednesday derives its name from this practice, in which the placement of ashes is accompanied by the words, "Repent, and believe in the Gospel" or the dictum "Remember that you are dust, and to dust you shall return." The ashes are prepared by burning palm leaves from the previous year's Palm Sunday celebrations.