The eTIR Implementation Guide for Customs is a practical reference developed by the UNECE TIR Secretariat to support customs administrations in adopting and operating the eTIR procedure. The guide explains how customs authorities can transition from paper-based TIR processes to a fully digital environment, covering key aspects such as data exchange with the eTIR International System, electronic guarantees, customs controls, information security, and procedures for handling exceptional situations. By providing operational guidance and practical examples, the document aims to promote a harmonized implementation of eTIR across Contracting Parties, helping customs administrations enhance the efficiency, transparency, security, and sustainability of international transit operations.