Abstract The claim drafting process, which is inherently related to inventions, is not exempt from difficulties. Prominent among these is vagueness, which can often be the chief characteristic of patent claims. This paper argues that such ambiguities may hamper the development and teaching functions of patent documents and can also distort infringement systems. It addresses legal issues related to patent claim construction, including the use of intrinsic or extrinsic evidence to clarify an ambiguous or vague claim. Confusion surrounding the use of expert testimony for determining the meaning of a claim is also highlighted. Largely based on the US law, the paper suggests ways to reduce claim ambiguity, such as the use of claim charts. Emphasis is placed on the clarity of the claims’ wording, because this acts as a safeguard against any infringement risk. In brief, constructing patent claims remains largely an unsettled and uncertain area of patent law. What really matters is the clarity of the claim language because definiteness, preciseness, conciseness and exactness are major guarantees of a patent’s validity.