Asthma is a disease with significant clinical impact and growing incidence, particularly in children. It is characterized by a complex interplay of environmental and genetic factors that affect airway structure and function, leading to recurrent and spatially heterogeneous airway obstruction. Conventional methods for evaluating lung function using spirometry and plethysmography are neither capable of assessing regional obstruction nor the regional dynamics of airway obstruction. MRI methods that exploit gas contrast agents have emerged as an attractive approach for evaluating heterogeneity and mechanisms of airway obstruction in the asthmatic lung without requiring ionizing radiation. Specific gas agents that show promise include hyperpolarized gases, oxygen enhancement, and fluorinated gases. Hyperpolarized (HP) helium-3 ( 3 He) and xenon-129 ( 129 Xe) MRI techniques in particular have enabled visualization of the airspaces of the lungs, including the large airways and lung parenchyma, during breath-held and dynamic respiratory maneuvers. This method has been applied to study disease progression, response to therapy, and asthma phenotypes. Diffusion-weighted MRI may be used to measure the dimensions of small airways and alveolar microstructure, allowing for the determination of structural changes associated with disease progression. Ultrashort echo time (UTE) MRI, an emerging technique, allows for rapid 3D acquisition of lung images at a resolution approaching that of CT. Patterns of poor ventilation observed on HP MRI identify regions of obstruction that may reflect underlying structural changes in the airway such as remodeling or chronic inflammation. HP MRI has also been used in conjunction with CT to perform image-guided sampling of airways leading to areas of poor ventilation in the lung, enabling the development of biomarkers of disease. These multimodality comparisons between CT and HP MRI may help evaluate regional structure-function relationships to assess causal mechanisms of disease and response to therapy and potentially to develop new disease phenotypes associated with clinical outcomes and healthcare utilization.