In this article we review the current state of knowledge in the field of responsive nanoparticles for aqueous-based systems. The review focuses on the use of stimuli-responsive copolymers that can either self-assemble into ‘soft’ nanoparticles or that are attached to the surface of solid nanoparticles. We first describe the most common methods for synthesizing the different responsive polymers used in the design of such nanoparticles, highlighting living radical polymerization techniques in particular. Subsequently, we give examples of how copolymers containing such responsive blocks can self-assemble into a wide range of ‘soft’ structures. We also depict the main techniques for attaching responsive polymers to the surface of solid nanoparticles and list advantages and drawbacks of each. Finally, for both soft self-assembled systems and solid core-polymer shell systems, we show specific examples of these systems used in a varied range of applications including drug delivery, smart emulsifiers, transport across membranes, sensors and coatings.