Use of the green fluorescent protein (GFP) of Aequorea victoria as a reporter for protein and DNA localization has provided sensitive, new approaches for studying the organization of the bacterial cell, leading to new insights into diverse cellular processes. GFP has many characteristics that make it useful for localization studies in bacteria, primarily its ability to fluoresce when fused to target polypeptides without the addition of exogenously added substrates. As an alternative to immunofluorescence microscopy, the expression of gfp gene fusions has been used to probe the function of cellular components fundamental for DNA replication, translation, protein export, and signal transduction, that heretofore have been difficult to study in living cells. Moreover, protein and DNA localization can now be monitored in real time, revealing that several proteins important for cell division, development and sporulation are dynamically localized throughout the cell cycle. The use of additional GFP variants that permit the labeling of multiple components within the same cell, and the use of GFP for genetic screens, should continue to make this a valuable tool for addressing complex questions about the bacterial cell.