The World Wide Web has become the carrier for the largest human knowledge repository in history. As its knowledge bases are growing towards a practically ‘infinite’ volume, Web-scale Knowledge Representation, Retrieval, and Reasoning (Web-KR) is becoming a real issue and an urgent task. Although the Web community has developed a number of knowledge representation languages and reasoning methods, when the volume goes Web-scale, existing approaches meet many challenging problems, such as scalability, inconsistency, uncertainty and dynamics. Hence, a unified approach to Web-KR needs to be developed. Following the successful 2010, 2011 and 2012 versions of the workshop under the same title in Toronto, Canada, Lyon, France, and Hawaii, USA (Here is a review on previous contributions of the Web-KR workshop during 2010-2012). This workshop aims to bringing together researchers from Web research, Artificial Intelligence (AI), high performance computing, cognitive science, knowledge management, and machine learning to discuss all issues of Web-KR in a synergistic setting. The main themes for Web-KR 2013 are construction of Web-scale knowledge bases, semantic search and reasoning (both deductive an inductive) over Web-scale knowledge bases. The workshop will be co-located with the 2013 ACM International Conference on Information and Knowledge Management (CIKM 2013) at San Francisco Airport Marriott Waterfront, Burlingame, CA, USA.