What is a log book?
The log book is the official document that holds the competition record of the vehicle. All inspections, and major incidents are noted in the book. It provides a history for the technical inspectors to check to make sure that any past damage has been properly repaired before allowing the vehicle to compete.
A common misconception is that simply possessing a log book means that the vehicle is legal to compete. Not so. Think of the actual words being used: "log book". It is simply a book that logs what this vehicle has done. Looking at a log book will tell you which events have been entered, as what damage occurred to the vehicle at those events. How well the vehicle placed is generally not recorded in these books.
The log book belongs to the car, not the driver. So make sure if you're purchasing a used rally car that the log book is present. If there's no log book or they seller says "Oh, I have it somewhere, I'll get it to you later." walk away.