This report will first describe the broad design specifications for the 1999–2006 survey including survey objectives, domain and precision specifications, operational requirements, sample design, and estimations procedures. Details of the sample design are divided into two sections. The first section (NHANES 1999–2001 Sample Design) broadly describes the sample design and various design changes during the first three years of the continuous NHANES (1999–2001). The second section (NHANES 2002–2006 Sample Design) describes the final sample design developed and applied for 2002–2006. Weighting and variance estimation procedures are presented in the same manner; however, to correspond to the public data release cycles, the weighting and variance sections are separated into those used for 1999–2002, and those used for 2003–2006. Much of this report is based on survey operations documents and sample design reports prepared by Westat. Documentation of the survey content, procedures, and methods to assess nonsampling errors are reported elsewhere.