Elie Wiesel's Night is a difficult book to categorize quickly, but since it is autobiographical, it cannot be classified as fiction. Instead, Night fits into one of the following genres: autobiography, memoir, or personal narrative. An examination of the characteristics will help determine the appropriate genre.

Autobiography:

• concerned about factual accuracy
• written (in some form) by the subject of the book
• tells the story of the author's life, or part of his life, in some kind of detailed chronology

Memoir:

• relatively informal in tone
• not as encompassing in scope
• written by the subject of the book
• concerned more with emotional truth than a series of facts

Personal Narrative:

• written by the subject of the book
• generally shorter than a book, perhaps only telling one story
• offers personal insight by the author

All three genres are written in first person by the authors (or ghost writer, in the case of an autobiography), as well.

This famous quote from Night suggests that this book is a memoir:

Never shall I forget that night, the first night in camp, which has turned my life into one long night, seven times cursed and seven times sealed....Never shall I forget those moments which murdered my God and my soul and turned my dreams to dust. Never shall I forget these things, even if I am condemned to live as long as God Himself. Never.

It is written in first person, contains an emotional truth, is informal in tone, and was written by the subject of the book about a specific period in his life. It is a memoir.

A quick examination shows that book sites such as Goodreads also  categorize Night as memoir, which is a subset of autobiography.