A scientifically sound environmental risk assessment is required for crops derived from modern biotechnology (also referred to as genetically modified [GM]) prior to unrestricted release into the environment.  The scientific principles underlying the environmental risk assessments completed for herbicide-tolerant and insect-protected GM crops commercialized to date are now being applied to crops currently under development that are modified for improved tolerance to abiotic stresses.  These principles, and the processes built upon them, have been shown to be sufficiently robust to provide the appropriate information for regulatory decision making and to ensure an adequate level of environmental protection.  This article describes the initial steps in the environmental risk assessment process and illustrates an approach that could be taken for GM crops tolerant to an abiotic stress (e.g., water, salt, cold, and heat).  The discussion below begins with an overview of the initial steps in an environmental risk assessment, known as problem formulation (US EPA, 1998 ).  A general overview describing how problem formulation has been applied for the first GM crops is presented next.  Finally, the approach is applied to a hypothetical drought-tolerant maize (Zea mays) product as an example of how problem formulation can guide the environmental risk assessment for a specific abiotic stress tolerant crop. Recent advances in functional genomics have led to the discovery of genes associated with tolerance to abiotic stresses such as cold, heat, water, and salt (Vij and Tyagi, 2007 ).  Some of these genes show promise in major crops like maize (Nelson et al., 2007 ) and rice (Oryza sativa; Hu et al., 2006 ).  As such, a discussion on planning an environmental risk assessment of GM abiotic stress-tolerant crops is timely.  Regulators are now confronting the challenges involved in evaluating data from these new and potentially beneficial products.  Products expressing stress tolerance phenotypes are now being widely tested in field trials around the world.  Very soon, technology providers will submit data and information on GM crops with stress-tolerant phenotypes to regulatory authorities for review that will include an environmental risk assessment as part of a request for commercial release.