This monograph reports a study investigating the roles of learning and development (L&D) professionals in Irish, UK European and US organisations. The study investigates the contextual factors influencing L&D roles in organisations, the strategic and operational roles that L&D professionals play in organisations, the competencies and career trajectories of L&D professionals, the perceptions of multiple internal stakeholders of the effectiveness of L&D and the relationships between context, L&D roles, competencies/expertise, and perceived effectiveness. We gathered data using multiple methods: survey (n=440), Delphi study (n=125) and semi-structured interviews (n=30). The analysis revealed that L&D professionals increasingly respond to a multiplicity of external and internal contextual influences and internal stakeholders perceived the effectiveness of L&D professionals differently with significant gaps in perceptions of what L&D contributes to organisational effectiveness. L&D professionals perform both strategic and operational roles in organisations and they progress through four career levels. Each L&D role and career level requires a distinct and unique set of foundational competencies and L&D expertise. Finally, we found that different contextual predictors were important in explaining the perceived effectiveness of L&D roles and the importance attached to different foundational competencies and areas of L&D expertise. We discuss the implications for theory, research and practice.