Incremental and Iterative Development

How they are different and Why You Should Be Doing Both
Article Summary: 

People get wrapped around the axle trying to understand the difference between incremental and iterative development. The Unified Process authors in the 1990s didn't help by indiscriminately calling everything iterative development. The two are different and must be managed differently. Successful teams do both at the same time, usually without thinking about it. Then someone starts thinking about it and does one without the other. Bad news follows.