Knowledge of the strengths of interactions between species in plant communities is of fundamental importance to our understanding of how communities are structured, although they are notoriously difficult to quantify. Techniques have recently been developed that allow the detailed enumeration of the strength of interactions between plant species within unmanipulated multispecies communities. Nonlinear regression analysis is used to fit competition models to long-term census data using natural variations in plant densities in lieu of manipulation. The models generated have been used to infer the intensity and importance of interactions as well as to analyse the effects of spatial and temporal variability. Theoretical work has begun to look at how different techniques for measuring competition perform in a range of systems, highlighting the importance of spatial scale. The lessons learned from applying these methods will enable improved estimation of the strength of competition in natural communities.