Changes in definitions are changes in the composition or classification of the components in the accounts. They are primarily made to:

Adapt the NIPA's to a changing economy;

Improve consistency and integration of the NIPA's with other accounts, such as BEA's I-O accounts, the Federal Reserve Board's flow-of-funds accounts, and the Bureau of Labor Statistics' productivity statistics; and

Improve consistency with international guidelines.

An example of a definitional change is the recognition of computer software as investment in the 1999 comprehensive revision. In the 2003 comprehensive revision,  the recognition of implicit services provided by property and casualty insurance and the allocation of a portion of the implicit services of commercial banks to borrowers represent other examples of definitional changes.