Atomic absorption (AA) has rapidly become the most widely used analytical technique for quantitative trace metal analysis. The technique is directly applicable to some 68 elements, including most of the metals and semi-metals, but excluding sulfur, carbon, halogens and inert gases. Atomic absorption is essentially a solution-based technique, with only very limited applications for the direct analysis of solids or gases. Advantages include specificity, speed, ease of use and excellent sensitivity. Detection limits are typically in the sub-ppb to low ppm range by weight in the sample solution. A vast amount of published 84AA methodology is now available, covering a wide range of application areas.