Evidence is accumulating that belowground soil organisms are strong drivers of the aboveground plant community. In this chapter, we examine how soil communities influence plant community assembly through priority effects, soil legacy effects, and niche modification. We discuss how different functional groups of soil organisms drive competitive interactions, species coexistence, and species turnover. We then explore how primary and secondary successional trajectories can be altered by soil communities and delve into the mechanisms by which soil communities can affect ecosystem restoration and biodiversity conservation. Finally, we discuss the role of soil biota in plant invasion and range expansion and how soil biota interact with global environmental changes to affect plant community composition. We conclude by outlining knowledge gaps and propose potential avenues for addressing these gaps via upscaling of measurements, enhanced experimental design, and the utilization of plant and soil organism traits.