The 1996 Act establishes a preventive wage norm, based on the expected evolution of the labour costs in three reference countries, namely France, Germany and the Netherlands. It refers for those three countries to forecasts drawn up by the OECD. In its "Economic Outlook", the Federal Planning Bureau (FPB) analyses in the chapter on the labour market, particularly since the 2007 edition, the monitoring of the “wage norm”. This analysis revealed the existence of different concepts of wage costs. This note aims to clarify and explain these concepts as well as the wage developments in these different meanings. It also seeks to raise questions related to these concepts