With a growing number of the WTO dispute settlement cases related to SPS measures, the appropriate standard of review and the specific legal standards to be applied under the provisions of the SPS Agreement have been gradually established and clarified by the WTO panels and Appellate Body. With respect to the obligations relating to a risk assessment and the principle of non-discrimination, the case law has focused mainly on the 'reasoning' or 'justification' provided by the regulating WTO Member and the panel’s examination in this regard centers on whether the Member has successfully provided ‘reasoned’ and ‘reasonable’ explanations. In keeping with this trend, the panel in Costa Rica – Avocados considered whether Costa Rica, the regulating Member, has provided reasoned and reasonable explanations with scientific basis for the risk assessment and the SPS measure at issue, concluding finally that Costa Rica acted inconsistently with the SPS Agreement. It is noteworthy that in reaching its conclusion, the panel thoroughly identified and referred to the previous SPS cases in which the issues of applicable standard of review had been addressed. In that respect, Costa Rica – Avocados constitutes an important precedent for understanding the nature and development of standard of review in WTO law and how it is to be applied in a specific case. This article outlines the legal issues raised in the Panel Report and examines matters such as the nature of the standard of review under the SPS Agreement, the relationship between the determination of ALOP and a Member’s discretion, and the obligation of the regulating WTO Member to provide explanation in the context of the principle of non-discrimination under the SPS Agreement.