This chapter presents a literature review on 4D Printed Composite Actuators for engineering applications. The recent integration of particle and fibre reinforcements into liquid crystal elastomers, hydrogels, and shape memory polymers enables the development of next generation actuators with advanced functionalities and significantly enhanced load-carrying capacity. Proofs-of-concepts considering the nature of the stimuli-responsive material are categorised, and the advantages of the particle and fibre reinforced devices are presented. The approaches are illustrated with examples, exposing their capabilities and limitations. Advanced functionalities and modelling techniques are summarised. The main challenges associated with implementing 4D printing technologies in two key engineering applications: soft robotics and morphing structures are discussed.