JACI: In Practice Editor David Khan describes the January issue, the theme of which is “Mast Cell Disorders”. Theme topics covered include the impact of molecular evaluations in the diagnosis and prognostication of patients with mastocytosis, diagnosis and management of patients with mast cell activation syndromes, management of mastocytosis and mast cell activation in children, and KIT-targeting drugs in the management of systemic mastocytosis. Dr. Khan then presents the Highlights of the Original Articles in the issue, which are on the topics of Mast Cell Disorders, Allergic Bronchopulmonary Aspergillosis, Asthma, Eosinophilic Disorders, Food Allergy, Hereditary Angioedema, Immunodeficiency, Immunotherapy, Insect Sting Allergy, and Urticaria