The main objective of the third version of the manual is to provide a set of standardized, technically sound and well documented, methods that would allow data or measurement precision and bias to be estimated and controlled, and thus promote the comparability of forestry field data across sites, research projects, and time. Although the concepts of standard operating procedures (SOPs), Quality Assurance activities, and quality control procedures have been deeply ingrained in many fields of research and manufacturing for decades, their utilization and acceptance in forestry has been minimal. Uniform, or standard, measurement methods are critical to projects that contribute data to some central data base for synthesis, integration, or assessment efforts. Consistent methods are particularly important to projects monitoring change to forest systems over time. Standardized methods, with known or estimable errors, contribute greatly to the confidence associated with decisions based on field data collections. The procedures are meant to serve as guidelines to the minimum activity necessary to provide high quality data for an integrated research program. Finally, the methods manual should serve investigators by simply reducing the amount of documentation required for an assessment of the data quality if they simply note that the procedures used, or proposed to be used, are those suggested in the manual.