Slate markers are based on measurable biochemical changes following alcohol abuse. Such markers can be either direct ethanol intake markers such as ethanol and ethanol metabolites, or the elevation of indirect biochemical markers that are representative of past ethanol intake. Trait markers are genetic markers indicating a degree of susceptibility of an individual for alcohol abuse. Although trait markers are generally in research and developmental stages, many slate markers of alcohol abuse are well established and widely available. There is increasing interest in the further development and understanding of clinically useful genetic markers. This chapter reviews both biochemical and genetic markers that could be employed to identify susceptibility to alcohol dependence, identify abuse, assist in the selection of effective therapeutic options, and monitor therapeutic compliance. These markers are summarized in Table 3.1. Please note that unless speci’ed otherwise the term alcohol denotes ethanol throughout this chapter.