Structural failure is a critically important design consideration in many engineering applications. Natureprovides a number of interesting examples of lightweight structural features that exhibit outstanding failure characteristics. Recent progress in additive manufacturing has facilitated precise control over geometric features, allowing for the implementation of bio- inspired structural designs on a layer-by-layer basis. Many bio-inspired materials including architected materials inspired by bones, shells, and bamboos exhibit remarkable resilience to fracture and failure. However, these strategies tend to involve materials-specific optimization, since the toughness enhancements strongly depend on the intrinsic interfacial properties of the specific materials used in the composites. In this work, we aim to understand the role of geometry in the failure characteristics of bio-inspired architected materials/structures. Our objective is to develop comprehensive design strategies for architected structures with enhanced fracture behaviors merely relied on geometric heterogeneity. We first study the use of bamboo-inspired void patterns to geometrically improve the failure properties of structures made from brittle polymers under flexural bending. Inspired by the void patterns in the axisymmetric longitudinal sections of natural bamboo, we explore the potential of varying spatial arrangement and size of voids to enhance higher damage tolerance. We then further study the effect of geometric voids on ductile materials. We show that crack blunting effect brought by architected voids magnified in brittle material system, while diminished in ductile material system. We proposed material’s intrinsic plasticity should be considered as a design parameter of architected voids. Then, with the deep understanding of utilizing bio-inspired heterogeneity to control the failure behavior of architected materials, we proposed a bio-inspired manufacturing method to fabricate non-deterministic architected structures. Specifically, we explore the idea of using simulated ‘swarms’ of simple agents to generate newdesigns of architected materials in a decentralized, bio-inspired manner, in which simple agents choose their own actions based solely on information in their immediate environment (no centralized control). The structures that result from these processes are built via the collective action of the individual agents, rather than a predetermined design. We build an integrated platform for determining what we refer to as “rule-structure-property” relationships, analogous to process-structure-property relationships in materials science. The integrated platform allows simulations of swarms of agents, showing how different rules for the agents and different environments result in different structural features. We then examine how these different structures behave mechanically, with a particular focus on the failure characteristics. The architected materials/structures design principles proposed in this thesis have the potential to be utilized in different engineering materials with different fabrication methods.