Hair disorders include hair loss, increased hair growth, and hair structure defects with increased breakage, as well as unacceptable cosmetic appearance, such as reduced shine, strength, curliness, and elasticity. It is the task of the dermatologist to choose the right diagnostic tool depending on the suspected clinical diagnosis. Moreover, certain tools are best suited for diagnosis in private practice, whereas others can only be used to monitor hair growth under treatment in clinical studies. The techniques can be classified as either invasive (eg, biopsies in scarring alopecia), semi-invasive (trichogram, unit area trichogram), or noninvasive (eg, global hair counts, phototrichogram, electron microscopy, laser scanning microscopy) methods. Further, one must differentiate between subjective and objective techniques. For the practicing dermatologist, body and scalp hair distribution by use of different grading systems, the hair pull test, and dermoscopy belong in the category of basic diagnostic tools. Basic techniques may be extended by computer-assisted phototrichogram and, in selected cases, by use of the trichogram and/or scalp biopsies. For research purposes optical coherent tomography, electron microscopy, biochemical methods, atomic force microscopy, and confocal laser scanning microscopy are optional tools. For clinical studies global photographs (global expert panel), hair weighing, phototrichogram, and different clinical scoring systems have proven to be objective tools for documentation and evaluation of hair growth and hair quality.