The crime of Driving Under the Influence (DUI) begins and ends with the work of a well trained law enforcement officer. These officers observe driving behaviors of DUI drivers, respond to 911 calls and accidents, observe the physical appearances and mannerisms of DUI drivers, administer field sobriety tests to drivers, and ultimately must decide whether the driver is under the influence of alcohol or drugs. The complexity of these tasks under difficult conditions requires the law enforcement officer to make many decisions that will affect the individual being investigated and ultimately the case against this person. Therefore the decisions made by the officer must only be based on a thorough and well crafted investigation. This book details the DUI investigation process from the initial observations of driving, the first contact with the driver, and the administration of field sobriety tests. This book takes an objective view of the DUI investigation process and what law enforcement must do to properly and ethically proceed with each phase of the DUI investigation. This book is a must for every DUI law enforcement officer and any individual in the field of DUI, including prosecutors and defense attorneys.