DNA microarrays are well suited as a tool for analyzing functional gene diversity as well as community composition in aquatic environments. Microarrays allow for the semiquantitative characterization of target genes by means of specific hybridization of labeled target gene sequences, amplified from the environment, to the corresponding oligonucleotide probes on the slide. Specificity and sensitivity are determined by the probe design. In their current implementation, environmental DNA microarrays are useful for analyzing microbial communities as well as for analyzing the presence of functional genes involved in larger biogeochemical processes, such as nitrogen cycling. Here, we lay out a basic protocol to analyze genes in the environment, which can be applied to most target genes of interest.