This book has several theme subjects which could be developed into full theme statements. The first theme subject widely covered in the novel is the idea of death. Obviously, the majority of the plot revolves around the death of Oskar's father in one of the Twin Towers. This also draws in the bigger picture of the many deaths that occured on September 11. There are also many other deaths (unrelated to Sept. 11) mentioned throughout the novel. The bigger picture focuses on those who have dealt with death in their lives and how they have survived (and are surviving) the loss.
Another theme subject of the book which coincides with death, is emotional trauma and coping. Oskar of course, as a child, is dealing with the loss of his father. Most of the plot focuses on Oskar's coping mechanisms. But always in the background is Oskar's mother. Though not a main focus, glimpses show Oskar and the reader as well, that she too is coping with a deep emotional trauma over the loss of Oskar's father.
Outside of the September 11th tragedy, Oskar's grandparents are also dealing with their own emotional trauma. His grandfather cannot bring himself to talk after his experience in WW2, but simply lives life with the words "yes" and "no" tattooed on his hands. His wife is struggling in a committed relationship with a man she no longer knows. Despite her love for him, he does not reciprocate, but she stays committed.
The story Extremely Loud and Incredibly Close has several themes.
The story is primarily about Oskar who loses his father in the Twin Towers' bombing. The themes of death and loss are quite obvious with Oskar, as is emotional trauma, which his father conveys on the five phone messages he leaves before he dies (which only Oskar knows about and has heard), and the trauma Oskar experiences in the loss of his father.
These three themes are also present with Oskar's grandfather. Before marrying Oskar's grandmother, he had been in love with his wife's sister. In Germany, during World War II, a bombing takes the lives of a number of people (Oskar's grandfather's family and Oskar's grandmother's family, including the woman Oskar's grandfather loves), but Oskar's grandmother survives, and Oskar's grandfather eventually marries her. However, when he finds that his wife is pregnant, he leaves: he cannot deal with any more loss so he tries to love no one and remain emotionally distant (though he never quite succeeds in severing the ties that bind him to others).
Mr. A.R. Black has experienced loss from the death of his wife, and William Black's father has died.
Many of the people in this story are dealing with death and loss; the story describes the different ways in which each deals with this loss.