Porphyromonas gingivalis is present in dental plaque as early as 4 h after tooth cleaning, but it is also associated with periodontal disease, a late-developing event in the microbial successions that characterize daily plaque development. We report here that P. gingivalis ATCC 33277 is remarkable in its ability to interact with a variety of initial, early, middle, and late colonizers growing solely on saliva. Integration of P. gingivalis into multispecies communities was investigated by using two in vitro biofilm models. In flow cells, bacterial growth was quantified using fluorescently conjugated antibodies against each species, and static biofilm growth on saliva-submerged polystyrene pegs was analyzed by quantitative real-time PCR using species-specific primers. P. gingivalis could not grow as a single species or together with initial colonizer Streptococcus oralis but showed mutualistic growth when paired with two other initial colonizers, Streptococcus gordonii and Actinomyces oris, as well as with Veillonella sp. (early colonizer), Fusobacterium nucleatum (middle colonizer), and Aggregatibacter actinomycetemcomitans (late colonizer). In three-species flow cells, P. gingivalis grew with Veillonella sp. and A. actinomycetemcomitans but not with S. oralis and A. actinomycetemcomitans. Also, it grew with Veillonella sp. and F. nucleatum but not with S. oralis and F. nucleatum, indicating that P. gingivalis and S. oralis are not compatible. However, P. gingivalis grew in combination with S. gordonii and S. oralis, demonstrating its ability to overcome the incompatibility when cultured with a second initially colonizing species. Collectively, these data help explain the observed presence of P. gingivalis at all stages of dental plaque development.