Soft actuators are one of the primary and critical components of a soft robot. Soft robots demand dexterous, fast, and reversible soft actuators that must be able to contract, extend, bend, and/or twist with favorable performance while delivering sufficient output forces. Pneumatic soft actuators are one of the most used types of soft actuators for soft robotic systems since they can be designed with internal deformable hollow chambers that dictate a desired output motion and can be directly fabricated using various additive manufacturing techniques. Pneumatic soft actuators based on a volumetric expansion and contraction are two main classes that include positive pressure soft actuators requiring compressed air to be activated or inflated upon their actuation and negative pressure soft actuators requiring a vacuum source for actuation. This chapter presents four-dimensional (4D)-printed pneumatic soft actuators that are fabricated directly using various additive manufacturing techniqu