From the BLS Handbook of Methods:

Description of the Survey

The CPS collects information on the labor force status of the civilian noninstitutional population 15 years of age and older, although labor force estimates are reported only for those 16 and older. Persons under 16 years of age are excluded from the official estimates because child labor laws, compulsory school attendance, and general social custom in the United States severely limit the types and amount of work that these children can do. Persons on active duty in the U.S. Armed Forces are excluded from coverage. The institutional population, which also is excluded from coverage, consists of residents of penal and mental institutions and homes for the aged and infirm.

The CPS is collected each month from a probability sample of approximately 60,000 households. Respondents are assured that all information obtained is completely confidential and is used only for the purpose of statistical analysis. Although the survey is conducted on a strictly voluntary basis, refusals to cooperate amount to only about 4 percent each month. (Another 3 to 4 percent of eligible households are not interviewed because of other failures to make contact.)

Ref: http://www.bls.gov/opub/hom/homch1_b.htm

This contrasts with the Establishment or Payroll Survey which samples employers s to estimate the number of jobs in various sectors of the economy.

Use the links above to view up to date charts of Payroll Survey data.

BLS FAQs on the Population Survey  

SGS Primer on Employment & Unemployment