Christians will be praying for the Muslim world and persecuted Christians over 30 days during Ramadan.
Ramadan is a time when Muslims fast from food and drink between the hours of sunrise and sunset. Open Doors says it is also a powerful time to pray for believers in Muslim-majority countries and the entire Islamic world.
It is inviting Christians to pray for the Muslim world from 9 July to 7 August, especially the countries that are on the Open Doors 2013 World Watch List of worst persecutors of believers.
This year Open Doors is marking 20 years of praying for the Muslim world during Ramadan but it emphasises that although millions of Christians have prayed over the last two decades, the challenges remain great.
"Of 1.6 billion Muslims worldwide, probably only one third know any Christians at all. But through our prayers, God can reach those we can't, and transform them with the power of His love," the organisation said.
Special 20th anniversary resources include key facts and figures about the Muslim world, prayer points from workers on the field, and testimonies of how God is working in the lives of Muslims today.
Find out more about the Open Doors resources at http://www.opendoorsuk.org/pray/30days.php