Higher plants and animals establish elaborate body plans with one end of the organism being different from another. Polar organisation is also of fundamental importance at the single-cell level, because mutations affecting cell polarity may cause severe body deformations. Hence, cell polarity is a central theme of biological research and much progress has been made towards our understanding of cellular polarisation along the shoot-root (apical-basal) axis of plants. By contrast, how polarity is established towards inner and outer lateral membranes of plant cells remains unresolved. Here, I propose to identify components controlling lateral cell polarity, employing the root epidermis of the genetic model plant Arabidopsis as an excellent system readily accessible for cell biological analyses. Root epidermal cells display polar nuclear movement towards the inner lateral membrane and proteins located at the outer lateral membrane. We will employ tools for visualization of these polar events that will enable us to A) perform forward genetic screens to discover signals and requirements for polar nuclear movement and outer lateral membrane polarity, B) apply forward and reverse genetics to unravel cytoskeletal requirements of lateral polarisation, C) employ live-cell imaging to reveal the dynamics of polarising events and D) combine genetic and cellular analyses with regulators of apical-basal polarity. Our work will uncover how a single cell separates and integrates polarising events along diverse axes. The proposed research is groundbreaking, as it will lay foundations for an understanding of lateral polarity establishment in plants. Finally, it will aid our understanding of how mechanisms underlying polarising events evolved differently in diverse multicellular organisms.