The Visa Bulletins are published monthly by the US State Department in order to notify the public of current and future immigrant visa availability for the various family- and employment-based immigrant categories, as well as for the diversity visa program.  

Visa backlogs typically always exist for family-preference categories, as well as for third-preference and "other-worker" employment-based categories.  Natives of China, India, Mexico, and Philippines are typically subject to longer backlogs due to the greater use of those countries' visa allocations.