This article discusses the US Court of Appeals for the Federal Circuit's decision in Lyons vs. American College of Veterinary Sports Medicine and Rehabilitation addressing a dispute regarding the proper owner of a service mark when there has been a departure from or change of membership in a group and both the departing party and the remnant group claim ownership of the mark. The ruling highlights the importance for ventures to enter into formal agreements memorializing ownership of a mark. This case also serves as reminder that it is prudent for parties forming a jointly owned entity to memorialize trademark ownership, especially following the possible dissolution of the entity or disassociation of one or more founders.