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Murray et al review recent developments in the design and analysis of group-randomized trials (GRTs), comparative studies designed to evaluate interventions that operate at a group level, manipulate the physical or social environment, or cannot be delivered to individuals. Examples of GRTs include school-, worksite-, and community-based studies designed to improve the health of students, employees, and residents, respectively. Just as the randomized clinical trial is the gold standard in public health and medicine when allocation of individual participants is possible, the GRT is the gold standard when allocation of identifiable groups is necessary. Moreover, they encourage investigators who conduct GRTs to become familiar with the developments and to collaborate with the methodologists who can strengthen the design and analysis of their trials.