Tremendous progress has been made in ontology learning, owing to the contribution of a variety of disciplines such as formal modeling, computational linguistics, knowledge engineering, machine learning, and Web intelligence. Nonetheless, the ultimate goal of developing a set of fully fledged ontology learning tools that can produce high-quality learning outcome is still far from reaching. A number of challenges need to be addressed before this field matures. Some open issues in ontology learning that are worthy of future research are summarized and potential solutions are suggested in the rest of this section.