Phase-change memory (PCM) has emerged in recent years as one among the most attractive technologies for future non-volatile solid-state memory. PCM relies on the reversible phase transition in chalcogenide materials between different states, i.e., amorphous and poly-crystalline, which are characterized by very different electrical properties. Multilevel storage, namely storage of multiple bits in a memory cell, is a key factor for the competitiveness of PCM technology in the nonvolatile memory market. This paper presents experimental characterization of multilevel PCM devices and addresses the feasibility and reliability issues of multilevel storage using adaptive program-and-verify schemes. ©2010 IEEE.