The plant rhizosphere is an important soil ecological environment for plant-microorganism interactions, which include colonization by a variety of microorganisms in and around the roots that may result in symbiotic, endophytic, associative, or parasitic relationships within the plant, depending on the type of microorganisms, soil nutrient status, and soil environment. Rhizosphere competence may be attributable to the differences in the extent of bacterial attachment to the root surface. We present results of the effect of various factors on the attachment to bean (Phaseolus vulgaris) and soybean (Glycine max) roots of some bacterial species of agronomic importance, such as Rhizobium tropici, Rhizobium etli, Ensifer fredii (homotypic synonym Sinorhizobium fredii), and Azospirillum brasilense; as well as the attachment capability of the plant growth promoting rhizobacteria Pseudomonas fluorescens and Chryseobacterium balustinum. Additionally, we have studied various bacterial traits, such as autoaggregation and flagella movements, which have been postulated to be important properties for bacterial adhesion to surfaces. The lack of mutual incompatibility between rhizobial strains and C. balustinum has been demonstrated in coinoculation assays.