During the course of a criminal investigation, the identification and comparison of human and animal hairs can be helpful in demonstrating physical contact with a suspect, victim, and crime scene. Hairs can provide investigators with valuable information for possible leads. In the manual, Microscopy of Hair Part 1: A Practical Guide and Manual for Human Hairs, the characteristics of human hairs and their significance to an investigation are described in detail. In this manual, the focus is on animal hairs. The manual begins with an extensive overview of the basic structure of hair. Hair is composed mainly of keratin and has three morphological regions: the cuticle, medulla, and cortex. It then discusses hair identification. Animal hairs are different in respect to human hairs. Animal hairs do not possess enough individual characteristics to differentiate individual animals from other similar animals. Animal hairs are classified into three basic types: (1) guard hairs that form the outer coat of an animal and provide protection; (2) fur or wool hairs that form the inner coat of an animal and provide insulation; and (3) tactile hairs (whiskers) that are found on the head of animal and provide sensory functions. This manual limited animal hair identification to those animals most likely to be encountered in casework, such as deer family and antelope, commercial fur animals, and domestic animals. Hair associations in casework should be subject to a confirmation process that has another qualified examiner review the match before a report is issued. The significance of a hair match is dependent on the distinct qualities of the hairs and the experience of the examiner. Figures, glossary and references