DNA microarrays are one of the new tools of genomics that have become quite commonplace in plant science research within the past decade. Essentially, DNA microarrays are an extension of the more traditional molecular biology technique of northern blotting. Unlike northern blotting, however, in which the expression of a single gene is monitored, DNA microarrays allow for the simultaneous monitoring of thousands of genes-or, in fact, potentially all of an organism's genes-in a single experiment. Most of the currently available plant microarrays are designed for crops species or the model plant, Arabidopsis; however, a microarray for at least one major weed species is currently available. Furthermore, CDNA-based microarrays prepared for one species can be used to investigate gene expression in related species. As the technology is maturing it is becoming much more accessible, and now is the time to begin utilizing microarrays in weed science research. Questions related to herbicide activity are particularly well suited for a microarray approach. Additionally, gene-expression profiling via microarrays can be used to address questions relating to weed biology, weed-crop competition, allelopathy, parasitic weeds, and biological control of weeds.