Paper has been known for thousands of years for its unique profile of properties: bendable & foldable, high mechanical strength, and its pore structure enabling pump-free fluid transport. Its production and recycling can nowadays be seen as technologically well-optimized. It has an environmentally friendly image and fosters the growing desire of the public for sustainable materials solutions. Despite its classical applications as print, packaging and hygiene paper, it has been in focus for several years in very challenging areas, e.g. in lateral flow tests (LFT), light-weight construction materials (e.g. as a honeycomb core in door leaves or shelves), as well as most recently in paper-based packaging as well as paper-based soft robotics. In this talk I will introduce our recent efforts in understanding and tailoring paper properties by controlled functionalization of the fiber and paper-sheet interfaces. Examples progress from the use of functional wax-polymer coatings to modulate barrier properties to cross-linking of polymers with paper fibers to introduce wet-strength properties in a sustainable fashion and the spatial control of interfacial attachment of polymers inside paper to gain 4D paper-based actuators.