This chapter deals with who is entitled to be a patentee, the rights that a patentee enjoys (which are some of the strongest within intellectual property law), the circumstances in which infringement actions might be brought, the defences that are available, and some points on exploitation practices. A key thread is the construction and interpretation of the patent and the inextricable link between the power conferred by the patent and questions of novelty and obviousness. This chapter also looks at sufficiency, the circumstances in which a patent may be revoked, and the risk of a claim for revocation of the patent.