Data from 25 experiments on seedlings of 43 tree species and hybrids show that ozone (O3) can reduce growth and photosynthesis at concentrations common in many areas of the USA. Seedlings have been primarily employed for such studies for logistic reasons, and will likely provide the greatest breadth of information for some time to come. However, a number of impediments limit application of seedling response studies to assessment of impacts on regional timber production. Large trees differ from seedlings in a number of ways, including C allocation and canopy structure, and methods must be developed to account for these differences if information from seedling studies is to prove useful to forest impact assessment. Understanding how competition mediates individual tree responses will require investigation of whether systematic differences of microclimate leaf morphology that exist across canopies affects foliage sensitivity to O3, and whether the maximum growth rates of genotypes are correlated with susceptibility to O3. Definitive information on these factors is necessary to assess impacts of O3 on stand development and diameter distributions in both multi‐ and single species stands. Of critical economic importance is whether O3 preferentially damages taller, more valuable individuals within stands and more valuable, faster growing stand types.