lunar month

A Shinigami's "Death Note" is a notebook with the power to kill the human whose name is written on it. All Death Notes follow a specific set of rules.

Written rules:
Before releasing his Death Note in the human world, Ryuk wrote the basic rules on the Note's first page. The rules were written in English because he was convinced this was the most popular human language. The basic rules are as follows:

The human whose name is written in this note shall die.

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.

If the cause of death is written within 40 seconds of writing the subject's name, it will happen.

If the cause of death is not specified, the subject will simply die of a heart attack.

After writing the cause of death, the details of the death should be written in the next 6 minutes and 40 seconds (400 seconds).

In addition to these basic rules, each volume of the manga has a page containing new rules or possible uses for the Death Note. In the anime series, each eyecatch (usually two per episode) contains a different rule written in both English and Japanese, similar to how they were revealed in the Japanese manga. These rules often serve to clarify the more esoteric uses of the Death Note that the characters discover on their own.