This document presents the findings of an extensive study of the leather tanning industry for the purpose of developing effluent limitations for existing point sources, standards of performance for new sources, and pretreatment standards of performance sources to implement the Clean Water Act. The study covers 158 facilities in SIC major group 3100 Leather and Leather products, and specifically in subgroup SIC 3111, leather tanning and finishing. Effluent limitations guidelines are set forth for the degree of effluent reduction attainable through the application of the best practicable control technology currently available (BPT), and the best conventional technology pollutant control technology (BCT) which must be achieved by existing point sources by July 1, 1984. Standards of performance for new sources (NSPS) set forth the degree of effluent reduction that is achievable through the applications of the best available demonstrated control technology, processes, operating methods or other alternatives. Pretreatment standards for existing and new sources (PSES and PSNS) set forth the degree of effluent reduction that must be achieved in order to prevent the discharge of pollutants that pass through, interfere with, or are otherwise incompatible with the operation of POTWs. Supporting data, rationale, and methods for development of the effluent limitation guidelines and standards are contained in this document.