The field of microbial ecology has grown tremendously with the advent of novel molecular techniques, allowing the study of uncultured microbes in the environment, and producing a paradigm shift: now, rather than using bacteria cultures for evaluating cell-specific questions, researchers use RNA and DNA techniques to examine more broad-based ecological and evolutionary constructs such as biogeography and the long-debated biological species concept. Recent work has begun to relate bacteria functional genes to ecosystem processes and functioning, thereby enabling a better understanding of the interactive role of bacteria in different and often-changing environments. The field continues to mature and will most likely make substantial contributions in the future with additional efforts that include metagenomics and genomics. Here we review progress in the application of molecular techniques to study microbial communities in freshwater environments.