An individual's right to privacy is addressed in the Constitution of the United States. States may have additional laws. Privacy law is about the protection and preservation of the privacy rights of individuals. This is a concern since businesses and government agencies have so much private info on people, and that info must be secure to protect privacy.
This will largely depend on your concerns. For example, in no state is it permissible for someone to open your mail or peer in your windows without your express consent. However, if your landlord accessed your apartment for an emergency repair while you were out; this would be acceptable.
In order to more thoroughly answer your question we would need to know what privacy laws you are seeking. There is the family privacy protection act that says it is unlawful to aquire and use someones personal data. There is also the personal identifying privacy protection act making it unlawful to find out ones social security number