This volume contains the papers presented at the 18th International Confer-ence on Algorithmic Learning Theory (ALT 2007), which was held in Sendai(Japan) during October 1–4, 2007. The main objective of the conference was toprovide an interdisciplinary forum for high-quality talks with a strong theoreti-cal background and scientific interchange in areas such as query models, on-linelearning, inductive inference, algorithmic forecasting, boosting, support vectormachines, kernel methods, complexity and learning, reinforcement learning, un-supervised learning and grammatical inference. The conference was co-locatedwith the Tenth International Conference on Discovery Science (DS 2007).This volume includes 25 technical contributions that were selected from 50submissions by the Program Committee. It also contains descriptions of the fiveinvited talks of ALT and DS; longer versions of the DS papers are available inthe proceedings of DS 2007. These invited talks were presented to the audienceof both conferences in joint sessions.