Methods to measure species richness and α-, β-, and γ-diversity are reviewed. A useful classification is α-diversity, the diversity of species within a community or habitat, β-diversity, a measure of the rate and extent of change in species along a gradient from one habitat to others, and γ-diversity, the richness in species of a range of habitats in a geographical area. Species inventories are frequently required for conservation management. Because a complete census is rarely feasible, the community must be sampled, and methods are needed to estimate via sampling the total taxa number present. A wide range of species richness estimators are described and their applicability reviewed. Models for species abundance, including geometric, log-normal, and broken stick are presented. Rarefaction techniques to compare species richness in communities sampled with differing effort are described. Methods to compare α-diversity between samples are described. Techniques to study community structure are introduced, and measures of niche size and overlap are presented. Similarity, indices are reviewed, and R code to measure niche overlap is presented.