The implementation of human resource (HR) practices (HRPs) is increasingly regarded as a cornerstone in the achievement of overall HRM effectiveness. This article addresses the role of the HR department in contributing to line managers' (LMs) effective implementation of HRPs. It does so by comparing the actions of HR departments in both effective and ineffective implementation processes in different firms. Its findings reveal that HR departments can make a difference by taking initiatives that foster LMs' implementation abilities, motivation and opportunities, such as deploying in-the-field HR specialists, framing practices in appealing ways, involving LMs in the development of HRPs and seeking CEO support, among others. By fleshing out these HR initiatives and linking them to the AMO framework, we build an inductive model that offers a more nuanced view of what HR departments can do to have their proposals effectively implemented by LMs.