Throughout evolution, biological organisms have developed efficient strategies to solve technical problems by synthesizing stimuli responsive materials that can change their structural and mechanical properties when exposed to an external stimulus. These materials can be used in a diverse range of applications including drug delivery, diagnostics, tissue engineering, biosensors, coatings and textiles. The stimuli can be endogenous, e.g. pH, redox and enzymes or exogenous such as temperature, magnetic or electrical signal and light. The mechanism in which the structural and mechanical changes occur is attributed to the molecule's nature and to the type of stimuli. In this presentation I will discuss the concepts of stimuli-responsiveness, the fundamental materials properties required and new strategies for designing stimuli responsive biomaterials.