Bacterial spreading through their surroundings via motility and growth plays a central role in agriculture, biotechnology, the environment, and medicine. These processes are typically studied in the lab in liquid cultures or on flat surfaces. However, many bacterial habitats, e.g., soils, sediments, and biological gels/tissues, are more complex and crowded 3D spaces. In this talk, I will describe my group's work using tools and approaches from soft matter, 3D imaging, and biophysical modelling to unravel how life in a complex 3D space influences how bacteria spread. We have developed the ability to (i) directly visualize bacteria from the scale of a single cell to that of an entire multi-cellular collective, (ii) 3D-print precisely structured collectives, and (iii) model their large-scale motion and growth in complex environments. I will describe how, using this approach, we are developing new ways to predict and control how bacterial collectives — and potentially other forms of "active matter" — spread large distances, adapt shape to resist perturbations, and regulate growth.