Abstract Industrially and scientifically speaking, the flax (Linum usitatissimum L.) plant is of great interest. The specific architecture of its stem makes it an exceptional model of vertical stability and slenderness, allowing the stem to resist in a notable way to lodging and buckling in the event of external solicitations. This chapter, dedicated to the multi-scale mechanical characterization of flax, is divided into two main parts. First, the specific architecture of the flax stem is described in order to understand why this plant develops singular characteristics and what lessons can be drawn from it for material science. The second part of the chapter emphasizes on the characterization of the performances of flax fibres and cell walls using a multi-scale and top-down approach, from the stem to the cell wall level. Although this chapter contains only examples from analyzes on flax fibres, the tools and methods presented may be used to study different elementary fibres, provided that their morphologies allow it, such as hemp or nettle. For each investigation scale, main interests and potential mechanical information are listed, as well as limiting factors.