ThisvolumecontainsthepaperspresentedatIJCAR2008, the4thInternational Joint Conference on Automated Reasoning, held August 12-15, 2008, in S- ney (Australia). The IJCAR conference series is aimed at unifying the di?erent research principles within automated reasoning. IJCAR 2008 was the fusion of several major international events: -CADE: The International Conference on Automated Deduction -FroCoS: The Symposium on Frontiers of Combining Systems -FTP: The Workshop on First-Order Theorem Proving - TABLEAUX: The Conference on Analytic Tableaux and Related Methods Previous versions of IJCAR were held in Seattle (USA) in 2006, Cork (Ireland) in 2004, and Siena (Italy) in 2001. These proceedings comprise 4 contributions by invited speakers, 26 research papers, and 13 system descriptions. The volume also includes a short overview of the CASC-J4 competition for automated theorem proving systems that was conductedduringIJCAR2008.TheinvitedspeakerswereHubertComon-Lundh, NachumDershowitz, AartiGupta, andCarstenLutz.Theirtalkscoveredabroad spectrum of automated reasoning themes, viz., veri?cation of security protocols, prooftheoreticalframeworksfor ?rst-orderlogic, automateddecisionprocedures and software veri?cation, and description logics. The contributed papers were selected from 80 research paper submissions and 17 system description submissions. Each submission was reviewed by at least three reviewers, and decisions were reached after two weeks of discussion through an electronic Program Committee meeting. The submissions, reviews, and discussion were coordinated using the EasyChair conference management system. The accepted papers spanned a wide spectrum of researchin automated reasoning, including saturation, equationalreasoninganduni?cation, automa- based methods, description logics and related logics, sati?ability modulo theory, decidable logics, reasoning about programs, and higher-order l