Autonomous motion and adaptability of microorganisms in fluids are hallmark features of living systems, fueling the emergence of active matter within the realm of soft matter physics. Notably, micron-sized synthetic self-propelled particles (SPPs) have emerged as a distinct class within this domain due to their unique ability to convert internal energy into directed motion, making them ideal models for studying inherently out-of-equilibrium systems. However, a significant challenge persists: the majority of existing synthetic SPPs are ill-suited for probing the governing principles of emergent collective behaviors observed in living systems, such as swarming, active turbulence, and living clusters, particularly in 3D real space. The ultimate aim of SynthAct3D is to pioneer a paradigm shift, transitioning synthetic active matter from the familiar territory of 2D experiments towards the uncharted terrain of 3D materials with advanced functionalities. This fundamentally driven, experiment-centric proposal seeks to unravel the core mechanisms behind emergent phenomena observed in living systems, employing entirely synthetic units. SynthAct3D focuses on two complementary goals, anchored in a novel experimental framework that combines innovative SPP designs, rigorous characterization, and high-speed confocal imaging: I. Phase behavior a. Investigate the influences of dimensionality (2D Vs 3D) and particle shape on the emergence of self-organization, both structurally and dynamically. b. Elucidate the role of particle propulsion and the microscopic nonequilibrium dynamics in dictating the macroscopic behavior of SPPs in 3D. II. Active materials a. Design reconfigurable 3D active materials (e.g. shape-shifting, and glasses) This research is expected to yield unprecedented insights into internally powered systems in 3D, paving the way for a new class of internally driven materials with applications in reconfigurable soft materials.