<p>The biological growth of fungal root structure, called mycelium, can be engineered to develop innovative fibrous and biocomposite materials. Mycelium materials have potential as sustainable alternatives to petroleum-derived materials for load-bearing applications. To realize this potential, there is an increasing effort dedicated to understanding the mechanics of mycelium materials. This work presents a systematic review of our current understanding of the mechanics of mycelium materials with a specific focus on structure–property relationships. The review first explores how the mycelium’s fiber network structure varies depending on whether it is grown as a two-dimensional (2D) membrane, a cellular foam, or as a matrix embedding biomass particles or a 3D-printed substrate. The mechanical behavior under tension and compression for three types of mycelium materials (i.e., membranes, foams, and composites) is discussed. The review showed that mycelium membranes exhibit nonlinear stress–strain behavior due to their dense and highly connected 2D fiber network, whereas mycelium foams behave like a bending-dominated soft solid due to their 3D porous structure. The composite mechanics is dominated by the densely packed structure of substrate particles and 3D-printed substrate geometry. Multi-scale modeling approaches for predicting mycelium mechanics are presented. A comparative analysis of the mechanical property space is presented to reveal that mycelium membranes show the higher stiffness and strength compared to other two materials due to their higher density. This review summarizes how microstructural features affect deformation and failure mechanisms of mycelium materials as well as highlights important knowledge gaps, providing a strong foundation to advance the field.</p> Graphical abstract <p></p>