Lumbar foraminal stenosis was suggested to exist as early as the 1800s; however, its importance faded when lumbar canal stenosis attracted attention. Subsequently, it was warned that lumbar foraminal stenosis should be considered as a “hidden zone.” Additionally, the importance of distinguishing foraminal stenosis from canal stenosis was reaffirmed when investigating the cause of lumbar nerve root symptoms. However, this condition is now widely recognized after the development of imaging modalities, such as computed tomography (CT) and magnetic resonance imaging (MRI); nonetheless, the accurate diagnosis of lumbar foraminal stenosis remains challenging. Lumbar foraminal stenosis is most commonly defined as a stenotic lesion extending from the medial edge of the pedicle to the lateral part. Conventional imaging examinations mainly include radiography and myelography; however, these imaging methods are unable to clearly visualize lateral lesions. Therefore, there is limited literature on lumbar foraminal stenosis. Subsequently, selective nerve root injection and CT have become popular, with MRI being the main diagnostic modality. The development of sequences such as 3-dimensional MRI, oblique coronal MRI, and diffusion tensor tractography has improved the diagnostic performance of imaging examinations. Thus, a better understanding of lumbar stenotic lesions among spine surgeons, in combination with more accurate imaging examinations, is expected to improve the accuracy of diagnoses, which in turn will help enhance the quality of treatment.