How Important is the Preamble of a Patent Claim?

By Barry R. Lewin

Patent claims are written with an opening statement, which is referred to as the preamble.  The preamble typically describes the type of claim (e.g., method, system, apparatus, or composition) and describes the nature of the invention.  It is followed by specific limitations of the invention.  But is the preamble actually a part of the content of the claim?

In a recent case, Shoes By Firebug LLC v. Stride Rite Children’s Group, LLC, the Court of Appeals for the Federal Circuit tackled the question of whether all or part of the preamble is actually a part of the claim.  In the case, two Firebug patents directed to illuminating footwear were being challenged. Claim 1 of each had the preamble “An internally illuminated textile footwear comprises:” with different limitations following the same preamble.  The question before the Court is whether the preamble limited the claim in any way.

The Court relied on several older opinions to note that there is no bright-line rule, but rather it depends on the entirety of the patent and what the inventors intended the claims to encompass.  The Court held that the preamble acts as a limitation when it “recites essential structure or steps”.  But the Court also held that the preamble is not limiting (and therefore not a part of the claim, such as when determining infringement)  when the rest of the claim “defines a structurally complete invention”.  For the two patent claims, after reviewing the remainder of the claims and the Specifications, the Court found that in one patent the preamble did provide structure and in the other patent it did not.

So how should preambles be written?  First, it is important to be sure that the remainder of the claim provides adequate structure or steps.  But an alternative is to put some requisite structure in the preamble if that makes the remaining limitations clearer.  The Applicant needs to then recognize the actual scope of the claim.  Either way, it is important to be sure that all limitations, whether or not in the preamble, are supported by the Specification.