This article analyses more or less 200 Concluding Observations adopted by the United Nations Committee of the International Covenant on Economic, Social and Cultural Rights (ICESCR). It covers a period that encompasses the work of the Committee between its 8th and 40th working sessions. The research is aimed at identifying the contribution of the International Labour Organization (ILO) to those Concluding Observations. Accordingly, only the part of such observations relating to fundamental workers' rights has been considered. Those rights are guaranteed by articles 6 to 10 of the Covenant. The authors come to the conclusion that input from the ILO to the UN ICESCR Committee monitoring work is essential and useful. They constitute a case for best practices in the land of inter institutional collaboration. The impact of the collaboration is namely, but not exclusively, apparent when one considers the evolving situation of atypical and marginal workers. The study also shows that inter institutional collaboration does not mean that each monitoring body has to renounce either to its specificity or explicit jurisdiction. On the opposite, such specificity promotes and increases the capacity of a monitoring body to tackle different aspects of fundamental workers' rights systemic violations. The study confirms the necessity to preserve intact the existence and the jurisdiction of different international law human rights monitoring bodies in order for them to contribute differently, although sometimes in a converging manner, to the protection of workers' labour rights.