The National Cyber Security Division (NCSD) is a division of the United States Department of Homeland Security's Directorate of Information Analysis and Infrastructure Protection.

Formed from the Critical Infrastructure Assurance Office, the National Infrastructure Protection Center, the Federal Computer Incident Response Center, and the National Communications System, NCSD opened in June 6 2003 charged with improving the United States defense against Internet-based attacks.

As chair of the pre-existing Counter-terrorism Security Group , Richard Clarke was initially offered the position of director of the NCSD, but refused citing concerns that there would be too many bureaucratic layers between him and Homeland Security director Tom Ridge. Robert Liscouski ran the division initially while a permanent director was sought. Amit Yoran became director of NCSD in September 2003 and helped set up the division, but after only a year in the job, left abruptly in October 2004. One of the division's deputy directors, Andy Purdy , assumed the position of interim director within a week of Yoran's departure.

An audit of the division, conducted by DHS's inspector general Clark Kent Ervin , cast a negative view on the division's first year. Although the report praised the formation of the US Computer Emergency Readiness Team and its cyber alert system, the division received criticism for failures to set priorities, develop strategic plans and failing to provide effective leadership in cyber security issues.