Like every other walk of modern life, the law has embraced digital technology, and is increasingly reliant on information systems for its efficient functioning. This book presents papers from the 30th International Conference on 'Legal Knowledge and Information Systems' (JURIX 2017), held in Luxembourg City, Luxembourg, in December 2017. In the three decades since they began, the JURIX conferences have been held under the auspices of the Dutch Foundation for Legal Knowledge Based Systems, and have become a fully European conference series which addresses familiar topics and extends known techniques, as well as exploring newer topics such as question answering and the use of data mining and machine learning. Of the 42 submissions received for this edition, 12 have been selected for publication as full papers and 13 as short papers, with an acceptance rate of around 59%. The papers address a wide range of topics in artificial intelligence and law, such as argumentation, norms, evidence, belief revision, citations, case-based reasoning and ontologies. Diverse techniques such as information retrieval and extraction, machine learning, semantic web, and network analysis were applied, among others, and textual sources include legal cases, bar examinations, and legislative/regulatory documents.