The authors present the new multi-threaded version of the state-of-the-art answer set solver clasp. They detail its component and communication architecture and illustrate how they support the principal functionalities of clasp. Also, they provide some insights into the data representation used for different constraint types handled by clasp. All this is accompanied by an extensive experimental analysis of the major features related to multi-threading in clasp. The increasing availability of multi-core technology offers a great opportunity for further improving the performance of solvers for Answer Set Programming (ASP).