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Shape memory polymer actuators have attracted great attention in the past few decades for developing soft robots, artificial muscles, and biomedical implants, among others. Herein, under a tutorial perspective, a series of shape memory actuators that display unidirectional movement upon exposure to specific external stimuli is explored. The mechanistic details associated with the movement of each system are also highlighted. In general, an overview of basic design principles, the chemical structure of molecular switches, the strategies used to achieve such controlled and unidirectional movement, as well as key experimental aspects, is provided. The most critical challenges of the existing devices that limit their practical applicability are also discussed. This is of utmost importance because such limitations must be overcome to fabricate micromotors that can generate complex movements, other than simple stretching/contraction or bending, to perform complex tasks.