Purpose of Review <p>This review aims to provide a comprehensive overview of the role of arginine and its metabolic pathways in regulating immune cell function, with a particular focus on their involvement in pulmonary inflammatory diseases. Additionally, it highlights recent advances in therapeutic strategies that target arginine metabolism as a potential therapeutic approach for the treatment of these conditions.</p> Recent Findings <p>Arginine is a conditionally essential amino acid that plays a pivotal role in numerous physiological processes, including immune regulation, tissue repair, airway tone modulation, and vasodilation. We found emerging evidence underscores that arginine metabolism is tightly controlled by various regulatory mechanisms, with two key enzymes—nitric oxide synthase (NOS) and arginase (ARG)—occupying central roles. These enzymes exert opposing yet coordinated effects within immune cells, contributing to the delicate balance between immune activation and resolution. Dysregulation of arginine metabolism has been implicated in the pathogenesis of several pulmonary inflammatory diseases, including respiratory infections, asthma, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis. Aberrant arginine metabolic activity in immune cells promotes either excessive inflammation or impaired immune defense, depending on the context.</p> Summary <p>Understanding the immunometabolic functions of arginine offers valuable insights into the mechanisms underlying pulmonary inflammatory diseases. Therapeutic modulation of the arginine metabolic pathway represents a promising strategy for controlling disease progression and improving clinical outcomes, paving the way for the development of novel targeted treatments.</p>