Additive manufacturing (AM) has the potential to revolutionize the way microscale devices are fabricated and designed. The unmatched geometrical freedom, low footprint, low material wastage, and fast prototyping ability offered by micro-AM are all key advantages over traditional photolithography routes. Despite these promises, many obstacles still remain, in particular for the synthesis of metal nano-architectures. At present, none of the reported micro-AM techniques allow fast and direct fabrication of complex 3D structures made of high-quality metals—the specification to be fulfilled for a significant impact in the field. This work contributes to the development of electrohydrodynamic redox 3D printing (EHD-RP)—a micro-printing technology—by leveraging its unique capabilities to address some of the aforementioned limitations. Controlling the microstructure of materials is a necessity for micro-AM applications in microtechnology. The thesis starts by establishing the wide range of microstructures and surface morphologies accessed in pure copper (up to > 99.9 at.%) via EHD-RP. In situ adjustments of the printing voltage allow grain size variations by one order of magnitude, changes in the compressive strength by a factor of two, and electrical resistivity control over an order of magnitude. Moreover, as a first step toward both—optimization of properties and site-specific tuning of microstructure—on-the-fly modulation of grain size with smallest segments of o 400 nm in length is shown. Based on transmission electron microscopy and atom probe tomography, it is suggested that the small grain size is a direct consequence of intermittent solvent drying at the growth interface at low printing voltages. In contrast, larger grains are enabled by the permanent presence of solvent at higher potentials. Finally, the process temperature strongly influences the deposition rate and thus dictates the deposited microstructure in a similar manner. This parameter, unlike the printing voltage, raises the deposition rate without increasing the electric field, thereby allowing layer-by-layer fabrication of dense microstructures. The second part aims at higher geometrical complexity. The fabrication of complex 3D shapes by EHD-RP is hindered by the autofocusing effect; the electric field used for droplet extraction from the printhead is concentrated at the depositing structure, thereby result- ing in the attraction of the charged droplets and geometry-dependent landing positions. The low level of concordance between design and printout rationalizes the simplicity of the designs reported so far and seriously impedes the development of EHD-RP, as well as electrohydrodynamic (EHD) printing of nanoparticle suspensions. To understand these deviations in the flight trajectory of the droplets, the electric field centrosymmetry is broken in a controlled manner using either external electrodes or the printed features themselves. Comparison of experimental outcomes with predictions of a finite element modeling model reveals the droplet characteristics and unveils how the product of droplet size and charge governs its kinematics entirely. The reliability of the simulated trajectories allows the calculation of optimized toolpaths that counterbalance the electric field distortion, thereby enabling the fabrication of geometries with unprecedented complexity. The final part paves the way to printing resolution below 100 nm, which opens exciting applications for micro-AM techniques. Unlike nanoparticle suspensions that tend to clog finer nozzles, solutions containing metal ions involved in the EHD-RP process do not restrict the nozzle size. Nonetheless, smaller droplets evaporate quicker and ultimately explode when the charge density reaches the threshold for stability—called the Rayleigh limit—ultimately turning the deposition into a spray regime. To address this issue, the boundary of droplet explosion is experimentally determined for various deposition voltages, nozzle sizes, and droplet flight distances. These experimental observations are in agreement with theoretical predictions that combine an analytical model for solvent evaporation with the time of flight as calculated by a finite element method simulation. Reducing the time of flight by shortening the nozzle distance prevents the spray regime—despite the use of smaller nozzles—and enables the thinnest out-of-plane nanowire (90 nm) achieved by EHD-RP. Finally, the 3D printing of a 30 μm-tall micro-tip comprising a 100 nm-wide dense nanopillar on its top allows direct materials characterization of the latter by atom probe tomography without additional preparation. This novel approach is able to quickly provide spatio-chemical information with unrivaled precision and opens new opportunities for materials development.