Mechanical instabilities, like buckling and snap-through instabilities, have been traditionally considered a sign of onset of mechanical failure. While they have been mostly avoided in man-made systems, nature often exploits them to generate fast actuation and high-speed motion in the plant and animal kingdoms. Examples span from micron-sized bacteria able to perform fast turns by buckling instability in the flagellar hook to Venus flytraps able to catch their prey with a snap-through trapping motion. Mechanical instabilities allow to store and rapidly release energy and to achieve high output power ampliﬁcation. These properties are appealing to the design of multifunctional devices where structural phase transitions can be sustained. In this talk, I will discuss two novel metamaterials exploiting mechanical instabilities to (i) control nonlinear transition wavefronts and to (ii) preprogram reversible sudden reconfigurations with a single pressure input, respectively. Finally, new functionalities for free thin-shell domes undergoing buckling instability will be presented. Both numerical and experimental approaches will be discussed and compared. Interesting applications such as fast sequential actuation, wave manipulation, and soft robotic distributed gripping strategies will be highlighted.