The structural organization of the dura and leptomeninges is reflected in its magnetic resonance (MR) imaging appearance in normal and disease states. Two distinct enhancement patterns are characterized: dura-arachnoid enhancement and pia-subarachnoid space enhancement. The dura-arachnoid pattern consists of curvilinear enhancement overlying the brain and immediately deep to the inner table of the calvaria, as well as along the falx and tentorium. Pial enhancement closely follows the brain surface into sulci and outlines the basal cisterns. Recognition of these enhancement patterns and other MR imaging characteristics may enhance the role of MR imaging in the detection, diagnosis, and follow-up of neoplastic and nonneoplastic disorders affecting the meninges. The focus of this article (Part I) is the MR appearance of the normal meninges and nonneoplastic causes of meningeal disease. Part II of this series will discuss neoplastic conditions affecting the coverings of the brain and spinal cord with an emphasis on pathways of disease spread.