IBA sites provide essential habitat for one or more species of birds and are important for breeding, wintering, and/or migrating birds.  IBAs may be anything from a few to thousands of acres and can include public or private lands (or both) and may or may not be protected.

To qualify as an IBA, sites must satisfy at least one of the following criteria. The site must support:
 

• Species of conservation concern (e.g. threatened and endangered species) 
• Restricted-ranges species (species vulnerable because they are not widely distributed) 
• Species that are vulnerable because their populations are concentrated in one general habitat type or biome
• Species, or groups of similar species (such as waterfowl or shorebirds), that are vulnerable because they occur at high densities due to their congregatory behavior 

Identification of a site as an IBA indicates its unique importance for birds and can be important on a global, continental, or state level. The IBA identification process provides a data-driven means for cataloging the most important sites for birds throughout the country and the world. The use of a hierarchical classification system further helps to establish priorities for conservation efforts.