Smart and functional polymers and polymer composites offer large application potential in areas such as sensors and actuators, energy generation and storage, filtration membranes and biomedical applications, among others. The successful development of applications rely both in the ability to proper tailor polymer properties, including microstructure, crystallinity and phase, and/or in the suitable choice of micro and nanofillers. An overview of the main challenges, strategies and results in the development of specific materials will be shown, together with some of their most interesting applications.