Introductory ecology courses include discussions of community structure, species diversity, and succession. Appreciation of sampling theory is essential to student understanding of these and other ecological concepts. For example, understanding community structure requires knowledge of what species compose the community as well as the abundance of each species. We developed web-based EcoSampler, http://www.departments.bucknell.edu/biology/courses/biol208/EcoSampler/, to facilitate student investigation of sampling theory and several ecological concepts. Using data from two Pennsylvania forests, an old-growth hemlock/yellow birch community and a long-uncut mixed oak/red maple community, EcoSampler allows students to sample these communities using area (quadrat) or distance (point-quarter) methods, with haphazard, random, or systematic sampling protocols. As students encounter new species within samples, images and natural-history information are offered. Students learn how to recognize when they have adequately sampled a community and a “time/effort” function permits students to assess the labor tradeoffs of sampling protocols. Output from EcoSampler includes absolute and relative measures of species density, frequency, dominance, and importance, size-class distributions, and dispersion, as well as species diversity. EcoSampler provides five assignments that can be completed in one, 3-hour afternoon laboratory period using high-speed internet-connected Windows (via Internet Explorer or Mozilla) or Macintosh (via Safari or Internet Explorer) computers. Assignments examine (1) potential for bias in haphazard, random, and systematic sampling protocols, (2) area versus distance sampling procedures, (3) species dispersion and successional trends based on size-class distribution analysis, (4) community structure as measured by species diversity, and (5) variation in species distribution due to topographic and edaphic factors.