Sitting en banc, the Court of Appeals for the Federal Circuit issued a major decision on patent law yesterday, affirming that there is a “written description” requirement, independent of the enablement requirement, for obtaining a patent. The Federal Circuit held that the written description requirement must be satisfied both for claims filed with the original patent application and claims that are amended or introduced during prosecution. The decision will likely disappoint those who were hoping for a major re-working of written description law, particularly inventors in the biotechnology and chemical fields where the requirement has often been an obstacle to obtaining and enforcing patent rights. The decision may also fail to satisfy anyone looking for additional clarity as to the precise scope of the written description requirement. Although the decision includes a clear holding that the written description requirement exists and is separate from the enablement requirement, there is little to clarify exactly how the Patent and Trademark Office (“PTO”) and courts are to enforce compliance with the requirement. This decision reinforces the need to draft patent applications with as much specific disclosure as possible, and to pursue a prosecution strategy which includes fall-back, narrower genus claims if the first broad genus claims cannot be supported.