LION 4, the 4th International Conference on Learning and Intelligent Op- mizatioN, was held during January 18-22 in Venice, Italy. This meeting, which continues the successful series of LION conferences, was aimed at exploring the intersectionsand uncharted territoriesbetween machine learning,arti?cial int- ligence, mathematical programming and algorithms for hard optimization pr- lems. The main purpose of the event was to bring together experts from these areas to discuss new ideas and methods, challenges and opportunities in various application areas, general trends and speci?c developments. Despite the economical crisis in 2009, which visibly a?ected the submission numbers of many conferences and workshops, we received an impressive n- ber of 87 submissions. As in previous years, we o?ered three di?erent paper categories for submission: (1) regular papers on original and unpublished work, (2)shortpapersonoriginalandunpublishedwork,and(3)worksfororalpres- tation only. Accepted papers from the ?rst two categories are published in the proceedings. Fromthe 87 submissions that wereceived,57 fell into the ?rstca- gory, 22 into the second one, and 8 into the last one. After a thorough reviewing process we accepted 19 regular papers (which amounts to an acceptance rate of 33%) and 11 short papers for publication in the proceedings. Additionally, nine regular paperswere accepted as shortpapers, and all eight submissions from the third category were accepted for presentation.