Called 'Madeleine', the book will be published next April, possibly to coincide with the fourth anniversary of her abduction. All proceeds will go to the Find Madeleine fund.
The McCanns are being represented by literary agent Christopher Little, after being introduced to him by Harry Potter author JK Rowling, who has donated thousands to fund the family's search efforts.
Speaking about the book deal, a source close to the McCanns said: 'Writing the book is proving to be a very painful experience for them, reliving all the awful memories and writing about their darling daughter when she is still not home. It is really the book they never wanted to write but they are desperate to keep the search for her going and see it as one of the best ways of raising money for the Find Madeleine fund.'
Kate McCann, 42, told reporters: 'There are several different reasons as to why I finally came to the decision with my husband Gerry to write and publish this book. This decision has not been an easy one.
'Many factors needed to be given thorough and careful consideration, not least the impact of such a book on the lives of our three children.My reason for writing is simple, to give an account of the truth. However, in the last few months with the depletion of Madeleine's Fund, it is a decision that has virtually been taken out of our hands. Every penny we raise through its sales will be spent on our search for Madeleine. Nothing is more important to us than finding our little girl.'
What do you think?
Are the McCann's right to publish a book about their daughter?
Should it be up to them to fund the search for her?