The measurement of forest structure has evolved steadily due to advances intechnology, methodology, and theory. Such advances have greatly increased our capacity to describe key forest structural elements and resulted in a range ofmeasurement approaches from traditional analog tools such as measurement tapesto highly derived and computationally intensive methods such as advanced remotesensing tools (e.g., lidar, radar). This assortment of measurement approaches resultsin structural metrics unique to each method, with the caveat that metrics may bebiased or constrained by the measurement approach taken. While forest structuraldiversity (FSD) metrics foster novel research opportunities, understanding how theyare measured or derived, limitations of the measurement approach taken, as wellas their biological interpretation is crucial for proper application. We review themeasurement of forest structure and structural diversity—an umbrella term thatincludes quantification of the distribution of functional and biotic components offorests. We consider how and where these approaches can be used, the role of tech-nology in measuring structure, how measurement impacts extend beyond research,and current limitations and potential opportunities for future research.