This issue begins with a summary of several Patent Trial and Appeal Board (PTAB) policy questions the U.S. Patent and Trademark Office (USPTO) has raised in an advance notice of proposed rulemaking. Next, we examine two recent appellate decisions. One is a Federal Circuit decision addressing the scope of inter partes review (IPR) estoppel and the allocation of the burden of proving whether IPR estoppel applies in a given circumstance. The second is a Federal Circuit decision addressing the requirement for showing written description support of a negative claim limitation, on which the U.S. Supreme Court recently denied review. Also, we examine several decisions addressing the requirement when proving obviousness to establish a rationale that would cause a person of ordinary skill in the art to combine prior art elements in a manner that satisfies the challenged claim as a whole. Finally, we briefly summarize the Supreme Court’s May 18, 2023, decision addressing enablement of antibody genus claims in Amgen Inc. v. Sanofi.