May is Religion Awareness Month (Celebrating People of Faith), International Nurses Day, Islam Eid al-Fitr and the Jewish Shavuot.

DateNational Day
01-May Orthodox Holy Saturday
01-May Twelfth Day of Ridvan - Baha'i
01-May Religion Awareness Month (Celebrating People of Faith) (1-31 May)
02-May Orthodox Easter Sunday
02-May Birthday of Guru Arjan Dev - Sikh
03-May Orthodox Easter Monday
03-May World Press Freedom Day
03-May Early May Bank Holiday
04-May Bank Holiday - ROI
04-May International Firefighters Day
07-May Vesak - Buddha Day - Buddhist
08-May World Red Cross and Red Crescent Day
08-May Laylatul Qadr (Night of Power) - Muslim
09-May Yom Yerushalayim (Jerusalem Day) - Jewish
10-May World Mental Health Awareness Week (10-16 May)
12-May International Nurses Day
13-May Ascension Day - Christian
13-May Our Lady of Fatima - Christian
13-May Eid ul Fitr - Muslim
15-May International Day of Families
17-May International Day Against Homophobia, Biphobia, and Transphobia (IDAHOBIT) 
17-May  Shavuot - Jewish holiday
21-May World Day for Cultural Diversity for Dialogue and Development
22-May International Day for Biological Diversity
22-May Declaration of the Bab - Baha'i
23-May Pentecost - Christian
23-May Birthday of Guru Amar Das - Sikh
24-May Bank Holiday - England, Wales, Scotland, Northern Ireland and ROI
28-May Ascension of Baha'u'llah - Baha'i
29-May International Day of United Nations Peacekeepers
30-May Trinity Sunday - Christian
31-May World No Tobacco Day 
31-May Spring Bank Holiday