Great Ormond Street Hospital is the last chance for children in the UK whose lungs are failing because of cystic fibrosis and other conditions. In a few severe cases each year, their only hope of survival is to undergo a risky step - a double lung transplant.
With extraordinary access to the medical teams and the families involved, this programme follows over a year the perilous but potentially life-changing process of giving a child new lungs and a new life.
Doctors only decide to list a child for transplant when they have less than two years to live with their own lungs. But new lungs - which can be rejected by the body - have a limited life-span. Neither doctors nor families can know how long they will last.
Children then have to live with the uncertainty of waiting for a matching donor lung to become available. As many as 25% die while they are still waiting.
For some lung transplant children, it is only after new lungs have arrived, that the greatest challenges begin.
Charlie is 9 years old and has cystic fibrosis. For most of his life he has managed to cope but in recent months his condition has rapidly deteriorated. Doctors and his family - and Charlie himself - will need to make a decision quickly.
Jess is 14, and was told she should be listed for a lung transplant two years ago. But she was too scared. She made her own decision to take a risk and delay the operation. But has she left it too late?
Chloe is 11 and has already been waiting for new lungs for nearly a year.
Louie is a few days short of his second birthday. Doctors are considering making him the youngest patient ever to have a lung transplant at Great Ormond Street.