Hello how may I help you? Can you tell me what the longest thing in the world is? I'm sorry I need more information. What is the longest book in the world? The longest book in the world is Moby Dick. How many pages is it? Moby Dick is 2532 pages long. What is the longest river in the world? The Nile river is the longest river in the world. How many miles long is it? The Nile river is 1245 miles long.