An introductory article in a series on testing textile fibres for mill workers, by textile chemist Dr. Louis J. Matos. It outlines the vegetable, animal and artificial fibre groups, the microscope and accessories needed, and gives formulas for sixteen chemical reagents. It also describes how to isolate fibres and mount them on slides, and how to apply reagents under a cover glass, with a few first identification examples such as cotton and caustic soda or copper solution tests.