During the past decades, the domain of trademark law and the scope of trademark protection have been expanded significantly. The flexible application of prerequisites for registration has paved the way for the recognition of a wide variety of signs as subject matter eligible for trademark protection. This includes single colors, shapes, sounds, smells, video clips, holograms, and even gestures. However, this expansion of the scope of trademark protection has been accompanied only by a partial expansion of the grounds for refusal relating to these registrations and the creation of defenses that permit unauthorized use in the interest of freedom of competition and freedom of expression. Hence, the expansion of trademark protection to non-traditional marks can have serious effects on market competition as these signs often protect products, or parts of products, per se. Likewise, the protection of these signs can prevent other socially valuable uses in related or unrelated non-commercial contexts. In this Introduction, the editors of this Book explain the risks posed by the protection of non-traditional trademarks, the causes for these risks, and the development of this type of protection, and lay groundwork for the more detailed discussion of the topic in the contributions to the Book.