Health consequences derived from alcohol drinking are a problem of increasing relevance worldwide. Ethanol toxicity is due essentially to its biotransformation products, acetaldehyde and different types of free radicals, which cause oxidative stress. Given that acetaldehyde and free radicals are highly reactive species is important to consider that, if generated in situ in a target tissue, they may cause toxicity. This book discusses the biochemistry, applications and safety concerns of acetaldehyde.