While considerable attention is paid to the legal aspect of implementation of European directives, the practical 'street-level' implementation of EU law remains to a large extent a 'black box'. This article sheds light on this black box with a study on the implementation of the Safety Data Sheets Directive in the Netherlands, Germany, the United Kingdom and Spain. This cross-national analysis reveals that different phases in the implementation process leave different traces. Although the member states correctly and completely transposed the directive, compliance by the regulated leaves something to be desired and enforcement by regulators is rare and varies considerably between and within the countries. This article looks into the factors that explain why even rules do not necessarily lead to even practices and argues for more attention for the phase of practical implementation.