Use of human nail as bio-indicators among various biopsy materials (urine, blood and other body fluids) is more attractive in assessing toxic and essential elements. This is in view of the fact that collection of nail samples is non-invasive. In addition, storage, preparations and analysis of the samples is also economical, and not susceptible to contamination. Vulnerable groups including children, pregnant women, elderly or chronically-ill are likely to benefit from this non-invasive procedure as a result of repeated or routine examinations. Use of nail tissue has therefore been proposed as a suitable method, especially in developing countries where analysis of toxic and essential elements is a challenge due to limited resources. Lead and cadmium are among the toxic metals of great concern because of their widespread use and they are also associated with serious adverse health effects. Children have been recognized as a special risk group whose toxicity levels depend on interaction with essential elements (zinc, iron and calcium). This book has therefore evaluated the concentrations of toxic and essential elements using nails of children as bio-indicators of risk exposures.