Allen v. Gillette is a United States Supreme Court case that was decided in 1888. The case involved a dispute between two parties over a patent for a razor. The plaintiff, Allen, had obtained a patent for a razor in 1871. The defendant, Gillette, had obtained a patent for a similar razor in 1878. Allen sued Gillette for patent infringement. The Supreme Court held that Gillette's patent was valid and that it did not infringe on Allen's patent. The Court reasoned that the two patents were for different inventions, and that Gillette's patent was for a new and improved razor. The Court also held that Allen's patent was not invalidated by the fact that it was not the first razor of its kind. The Court's decision in Allen v. Gillette established the principle that a patent is valid even if it is not the first of its kind. This principle has been applied in numerous cases since then, and it is still an important part of patent law today.

Justice Field delivered the dissenting opinion in Allen v. Gillette, arguing that the majority's decision was contrary to established precedent and would lead to a dangerous expansion of patent law. He argued that Congress had not intended for patents to cover improvements made on existing products, as this would effectively grant monopolies over entire industries rather than just individual inventions. Furthermore, he noted that such an interpretation of patent law could potentially stifle innovation by preventing others from making similar improvements upon existing products without fear of infringement suits. Finally, Justice Field asserted that if Congress wanted to expand the scope of patent protection it should do so explicitly through legislation rather than relying on judicial interpretation alone.