In recent decades, multilateral and regional trade negotiations and unilateral liberalization have substantially reduced tariff rates. Non-tariff measures (NTMs), however, represent a growing challenge for exporters and policy makers. The ability to gain and to benefit from market access depends increasingly on compliance with trade regulatory measures such as sanitary requirements and goods standards. The United Nations Conference on Trade and Development (UNCTAD) has been actively involved in research and activities on issues related to non-tariff measures. The purpose of this publication is to provide guidelines to enable data collectors to harmonize the data collection process and to minimize uncertainty during the process of categorization and classification.