This chapter considers a tolerance selection approach and shows how tolerancing influences some gear pair performance parameters. Tolerances that are seemingly negligibly small in comparison to nominal gear dimensions greatly affect gear drive performance and product cost. Comprehensive gear drawing specification is critically important. A gear drawing specification must completely define gear geometry, accuracy level, reference dimensions, all critical dimensions with tolerances, gear inspection dimensions, surface finish, material data including its grade, heat treatment, and post-machining surface treatment. A gear specification table for gears with asymmetric teeth contains geometry parameters of both drive and coast tooth flanks. Gear accuracy selection depends on gear drive application, operating conditions, and technical and market performance requirements. Gear accuracy is defined by a set of tolerances. A wide operating temperature range noticeably changes gear drive dimensions and may greatly affect tolerance analysis results in case of dissimilar materials for gears, gear housing, and other gear drive assembly parts.