On January 12, 2016, the Patent Trial and Appeal Board (PTAB) designated as precedential a previous Board decision in Westlake Services, LLC v. Credit Acceptance Corp., CBM2014-00176, Paper 28 (PTAB May 14, 2015), clarifying the application of estoppel under 35 U.S.C. § 325(e)(1).  In the decision, the Board held that estoppel applies on a claim-by-claim basis.  Specifically, the Board held that “[b]y its terms, estoppel is invoked under Section 325(e)(1) as to ‘a claim in a patent’ that ‘results in a final written decision under’ 35 USC 328(a).”  In determining whether estoppel applied to a second CBM review in view of a Final Written Decision issued in an earlier CBM review, the Board declined to terminate the second CBM review because the Final Written Decision only ruled upon the patentability of claims not at issue in the second CBM review.  In the earlier CBM review, the Board did not institute review of the claims before the Board in the second CBM review.  Because these claims did not result in a Final Written Decision under 35 U.S.C. 328(a), the Board held that estoppel under Section 325(e)(1) does not apply to those claims.