In the vast majority of cases, they are the same (or nearly so). However, unlike ZCTAs, ZIP Codes can cross state and municipal boundaries, and are prone to frequent change. There are definitely instances where ZIP Codes are added by the USPS, as is the case with "expansion" ZIPs, to accommodate rapidly growing areas. There are also ZIP Codes that are used for commercial purposes that have no boundaries, per se, but are rather single points on a map. Furthermore, there are ranges of ZIP Codes that have identical point locations such as post office box stations.