In this talk, I will describe Project Halo, a large-scale research program in artificial intelligence sponsored by Paul Allen’s Vulcan Inc.. Project Halo has three parts: 1) an expert system called AURA for knowledge formulating and question answering in science; 2) an advanced reasoning system called SILK for default and higher-order inference; and 3) a social semantic web platform called Semantic MediaWiki+ (SMW+) for effectively building the large basic knowledge base that is necessary for the other two parts to work. I will briefly describe the first two of these parts, but I will spend most of my time describing Project Halo’s work in on SMW+. SMW+ combines semantic web technology and wiki-based social mechanisms, and marries the structure and flexibility of a database to the crowd sourcing power of a wiki. I will show several examples of SMW+, and conclude by describing Vulcan’s Ultrapedia prototype, in which we show what Wikipedia might look like if it was built with a semantic wiki.