Testing Human Resource Management (HRM)’s effect on organisational performance has been a core part of HRM research over the past 25 years. Whereas pioneering studies in the field neglected the mechanisms explaining this relationship, treating it as a ‘black box’, in the last decade the focus has been on examining the mediators of this relationship. Most recently, a series of reviews has been more critical of the field, particularly highlighting its diversity and underplaying of employee involvement, a concern central to its inception. This paper assesses these mediation studies in the light of these concerns, which provide criteria by which I summarise them and assess the extent to which they have advanced the field. The analysis demonstrates that the main problems of the black-box studies remain: the misalignment of the use of additive indexes and the theory of synergistic relationships, confusion over analysis methods, inadequate justification of the selection of practices in the empirical investigations, and under-representation of employee involvement. The researchers continue to present the field as a unified one. However, since the majority of studies are centred on high-performance work systems, there is a clear schism across them between these studies and those centred on high-involvement management. The paper reinforces the importance of this distinction, on the basis that a high-performance work system is a technology, a set of sophisticated personnel practices, whereas high-involvement management is a managerial philosophy or orientation towards fostering employee involvement. The paper concludes by suggesting ways of overcoming the recurring problems in HRM–performance research, and how these vary between the two perspectives.