Histiocytic disorders encompass a diverse and rare group of conditions including histiocytic neoplasms such as Langerhans cell histiocytosis (LCH) and non-LCH, and hyperinflammatory diseases like hemophagocytic lymphohistiocytosis (HLH). Over the years, significant progress has been made in our understanding the pathogenesis, and treatment of these disorders, leading to improved outcomes for patients. This three-article series, commissioned by the Histiocyte Society, highlights progress in histiocytosis research and care.