This EUROMECH Colloquium will focus on recent advances in analytical, computational, and experimental approaches for the multi-scale modelling and optimisation of meta-materials and meta-structures. Bringing together experts from applied mathematics, physics, and engineering, the event aims to bridge the gap between Solid Mechanics and mathematical modelling communities. Topics include non-classical theories, anisotropy, and multi-physics effects, especially when scale separation fails or manufacturing constraints are critical. Emphasis will be placed on structural optimisation across different scales, including applications involving novel architectures, additive manufacturing, and generalised continuum models for designing complex, multifunctional materials.