Janus colloids are functional particles consisting of two surfaces (or internal materials) with distinct physical or chemical properties in the same particle. Owing to their amphiphilic nature, Janus colloids composed of both hydrophilic and hydrophobic faces provide a powerful tool to generate functional surfaces and to manipulate the properties of interfaces. Amphiphilic Janus colloids have shown promising applications as particulate surfactants in oil/water separation, as interfacial compatibilizers in polymer blends, and as assembly blocks in robust coatings with unique wettability. In this Feature Article, we summarize recent advances in engineering interfaces by using Janus colloids.