The Suggested Upper Merged Ontology (SUMO) is an upper level ontology that has been proposed as a starter document for The Standard Upper Ontology Working Group, an IEEE-sanctioned working group of collaborators from the fields of engineering, philosophy, and information science. The SUMO provides definitions for general-purpose terms and acts as a foundation for more specific domain ontologies. In this paper we outline the strategy used to create the current version of the SUMO, discuss some of the challenges that we faced in constructing the ontology, and describe in detail its most general concepts and the relations between them. Categories & Descriptors --- I.2.4 [Knowledge Representation Formalisms and Methods]: Artificial Intelligence -- representations (procedural and rule-based), semantic networks. General Terms --- Documentation, Languages, Standard-ization, Theory. Keywords --- Ontologies, Knowledge Interchange Format.