By Caroline Wyatt
BBC News, Paris
A new tax has come into effect on all flights leaving France, with money going to humanitarian projects in developing countries.
Few European nations have signed up to the French proposal
It is expected to raise 200 million euros (£130m) for development aid in its first year of operation.
The levy is one euro on short haul flights in Europe, rising to 40 euros for first-class long-haul flights.
The project was personally backed by French President Jacques Chirac, who wanted the wealthy West to follow suit.
Added together, the tax will raise millions in development aid, with the money going towards an international medical fund to fight Aids, TB and malaria.
The fund, known as Unitaid, will bulk buy medicines for countries, especially in Africa, which could not otherwise afford them.
The other nations who have signed up include Brazil, Chile, Cyprus and Norway, but few of France's nearer neighbours.
The UK has said that while in principle it supports the idea, it already has a similar levy in place - raising money for debt relief.
Most airlines have lobbied against the idea, claiming that an extra tax on tickets at a time of rising fuel costs is unfair on the airlines.