A Death Note is a book held by a shinigami which has the power to kill people if certain conditions are met. All Death Notes follow a long set of specific rules, and the writer revealed a few of these rules with each volume of the manga in Japan.


Written rules
Before releasing his Death Note into the human world, Ryuk wrote some of the more basic rules on the first page in English, because he believed that English was the most popular language in the world. The rules written by Ryuk are the following:

1.The human whose name is written in this note shall die.
2.This note will not take effect unless the writer has the subject's face in their mind when writing his/her name. Therefore, people sharing the same name will not be affected.
3.If the cause of death is written within 40 seconds of writing the subject's name, it will happen.
4.If the cause of death is not specified, the subject will simply die of a heart attack.
5.After writing the cause of death, the details of the death should be written in the next 6 minutes and 40 seconds (400 seconds).