What religions celebrate Ash Wednesday?

Answer 1

Ash Wednesday is a Christian festival - so the religion that commemorates Ash Wednesday is Christianity.

As to what denomination of the Christian Church, most denominations regard the 40 days (not including Sundays) that lead up to Easter Day, called Lent, as a time for penance, self-examination and reflection, and the start of this time, Ash Wednesday, is therefore significant.

It is not a case of 'which denominations celebrate Ash Wednesady and which do not' as there is a great range of attitudes to the day. Some denominations, notably the Roman Catholics, some Anglicans, Orthodox and so on regard it as an important day where services involving 'ashing' (wearing of an ash cross on the forehead as a symbol of penance) are still commonplace. However, many other denominations recognise Ash Wednesday but do not regard it as anything special or significant. These may include some of the more evangelical denominations where scripture, and not tradition, is regarded as much more important.

Answer 2

Christianity.