The CEOS Systems Engineering Office (SEO) was established in April 2007 to facilitate the development of CEOS space constellation plans. The SEO provides systems engineering leadership, provides a framework for coherent architecture plans, and provides decision support tools for trade studies and the assessment of execution options to maximize the probability of their implementation. While the CEOS Constellation Teams and Working Groups are diverse and have multiple goals, selected commonality and a consistent systems analysis approach will strengthen plans and improve coordination and collaboration toward the realization of a Global Earth Observing System of Systems (GEOSS). To date, the SEO technical efforts include requirements definition, constellation assessment, gap analyses, and future architecture development. In addition, the SEO fosters communications among CEOS partners by coordinating and participating in CEOS Constellation Workshops and Working Group meetings, developing tools for file sharing and action item tracking, developing visualization products for educating the global Earth Observation community about CEOS, and supporting the content development and management of the CEOS website. The SEO looks forward to its role in CEOS and working with the member groups and agencies.