Since the U.S. Supreme Court’s ruling in Nautilus, Inc. v. Biosig Instruments, Inc., several courts have reviewed the indefiniteness of patent claims under the new “reasonable certainty” standard. Although it is difficult to gauge the full impact of the changed standard for indefiniteness, it appears that some types of claim terms are more vulnerable to being found indefinite than others. Patent practitioners can use the recent decisions on indefiniteness to shore up weaknesses in patent applications and claims or to exploit potential weaknesses in a competitor’s patent.