This collection of essays focuses on all aspects of the emerging field of pharmacogenomics except the science that underpins it. This omission is understandable because the science of pharmacogenomics is currently clouded by uncertainty. Pharmacogenomics refers to the use of genomic tools to understand differences among people in their responses to drugs, either in terms of efficacy or in terms of adverse effects. It is assumed that many of these differences derive from specific DNA-sequence variants. Yet this assumption is largely unproved. Moreover, we have little understanding of the nature or frequency of such functionally important variants or of their distribution in different populations. Still, the paucity of data has not prevented prominent academics and executives in the biopharmaceutical industry from making sweeping statements about how pharmacogenomics will bring about the era of "personalized" medicine. Such statements offer an irresistible starting point for considerations of the social and ethical implications of pharmacogenomics. Scientific uncertainty does not provide much on which to build an essay. The one indisputable fact about pharmacogenomics is that it offers a possible solution to immense clinical problems that currently have no solutions - namely, serious adverse drug effects and the poor response of considerable numbers of patients to the available treatments for a given condition. It is therefore not surprising that the chapter called "Integration of Pharmacogenomics into Medical Practice" is the crispest essay in the book. The authors of this chapter offer concrete examples of success stories in which pharmacogenomics may have helped identify subgroups for specific cancer treatments. Other chapters offer fascinating glimpses into fields that may not be familiar to geneticists, genomicists, or clinicians and that have yet to be defined in relation to the anticipated effect of pharmacogenomics. For example, there are two detailed chapters about the legal implications of pharmacogenomics, one on intellectual-property law and the other on potential liability issues. These chapters show that it is possible to be prepared for a variety of alternative scenarios, depending on what the science indicates. What is really striking is the diverse ways in which the prospect of pharmacogenomics is influencing social science. Several forceful chapters focus on race - what it means, how it is defined, and how pharmacogenomics may influence its relation to issues of social justice, such as discrimination and equality of access to health care. These chapters are particularly speculative, and their conclusions may change as the science of pharmacogenomics progresses, particularly if this science does not result in personalized medicine within the next several years. Still, they will be informative for geneticists or genomicists and provide a reminder that many people outside this field are going to be paying a lot of attention as discoveries about human genetic variation and drug response are reported.