The remediation and revegetation of tailings sands produced during the extraction of bitumen from the Athabasca tar sands present numerous challenges, from the sheer volume of tailings produced to the quality of the tailings (toxicity, high salt, low nutrients) to support growth. The objective of this work is to characterize alder-Frankia symbionts as potential candidates for the remediation and revegetation of composite tailings (CT). A variety of alder species have been examined for seed germination efficiency, and for growth in CT sands. The most robust species, Alnus rugosa and A. crispa, are indigenous to northern Alberta. Species of Frankia have been evaluated for survival and growth under high salt conditions, as well as in toxic naphthenic acids, and one strain, designated F9, was selected for further study. Survival and growth of alders inoculated with Frankia, the mycorrhizal fungus, Hebeloma, or both were evaluated in greenhouse assays using composite tailings (CT) sands obtained from the Athabasca tar sands operations. In addition, the microbial community structure and activity in CT soils containing Frankia inoculated species of alder have been examined. Frankia F9 was specifically detected using PCR amplification, in the endophyte community from alders that had been inoculated with the strain. Enrichment cultures derived from alder-Frankia planted CT sands were able to degrade a commercial naphthenic acid mixture. The results clearly demonstrate that alders are capable of survival and growth in CT sands, and that their presence has a positive impact on the diversity and activity of the indigenous microbial community. Also, alders that had received the specific Frankia inoculum retained this bacterium in their internal tissues, as demonstrated by strain-selective PCR analysis, indicating that a specific strain of symbiont can be successfully introduced into the alder during development. Current work includes the continued refinement of molecular techniques to monitor and track the specific Frankia inoculum, and the evaluation of the effectiveness of the alder-Frankia symbionts in field trials on CT residues.