Improperly prepared turkey gives harmful bacteria the opportunity to grow and cause foodborne illnesses.
Although there are several ways to prepare the turkey its internal temperature should reach 165˚ Fahrenheit. This should be determined with a food thermometer. Check the temperature in the innermost part of the thigh and wing and the thickest part of the breast. Different cooking methods as well as the weight of the turkey will impact how long it will take to prepare.
If you are planning on roasting your turkey this holiday check out this link for turkey safety basics: http://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/poultry-preparation/turkey-basics-safe-cooking/CT_Index and http://www.cdc.gov/features/turkeytime/