The Archbishop of Canterbury has given Alpha bible study courses their most glowing endorsement yet by launching the latest series.
Alpha says the courses have introduced 1.5million people to Christianity.
However, the marketing methods used to sell the courses have been criticised for aligning them too closely with the world of commerce.
Speaking at the launch in Holburn, London, Dr Rowan Williams praised the group for boosting congregations.
Alpha is set to launch a new advertising campaign with a £1m budget.
Meaning of life
The bible sessions, which are advertised as a chance to explore the meaning of life, typically start with a supper, include a short service, a talk and group discussion.
Topics include asking whether Christianity is boring, untrue and irrelevant and discussions on how to pray.
The courses are held in churches, prisons, among students, young people and people in the forces.
BBC religious affairs correspondent Robert Pigott said some claim that Alpha's use of modern marketing techniques aligns it too closely with the world of marketing and commerce.