The claims of a US Patent is the most important section, and is curiously listed in the end of most patent documents. The claims to a US Patent are what an engine is to an automobile. The specification is the chassis, the background is the paint job (sort of) and the abstract is the cup holder.

To read the claims of a US Patent you should think of the BB Gun contest at your county fair (think Mr and Mrs. Smith with Angelina Jolie and Brad Pitt). In order to win the stuffed teddy bear you have to hit all ten targets. Hit nine of them and you go home empty handed.

The same holds true for the claims of a US Patent. All of the constituent elements must be found in the competing article to make a case for infringement (with the small exception for the Doctrine of Equivalents to be discussed in a later article). Miss one of those listed constituent elements, and you do not have infringement.

Typically, the first independent claim, or claim 1, will give you a good idea if there is infringement. If you find all of those constituent elements in claim 1, read no further. All of the underlying claims (e.g. claims 2...) are not extremely instructive on patent infringement.

For instance, let's say that claim 1 comprises: 1.) an ink cartridge, 2.) an ink cartridge housing, and a 3.) cap (i.e. a pen). And let's say that the product you want to sell is a pen with an ink cartridge, an ink cartridge housing, and a cap. As per US Patent Law, your selling, making, using, licensing, and importing of that product would constitute patent infringement because all three constituent elements are found in your device.

Now suppose you would like to sell the same device without the cap. Since claim 1 of the US Patent specifically lists a cap as a constituent element, there would be no infringement. For this reason, it is absolutely crucial to decide early on how a competitor might sell similar products to your invention. Are there parts and components she might be able to leave out in order to get around your patent?

For these reasons, you need to discuss with your patent attorney what the core novelty of your invention is and how you anticipate marketing the same. And you should do this mindful of what a clever competitor can leave out of his competing products to adroitly avoid patent infringement.