Abstract: Using non-crimp fabrics (NCF) as reinforcements in liquid composite moulding (LCM) is suitable for volume production of high-performance composites with low capital investment. High-quality and defect-free NCF preforms are essential for the mechanical performance of NCF composites produced through LCM. This paper reviews the research progress on NCF forming regarding material characterization, numerical modelling, defect mechanisms and mitigation approaches, with issues and challenges discussed accordingly. The review indicates that the forming behaviour of NCFs at macro-scale is closely related to their architectures at meso- and micro-scales due to the multi-scale nature of NCFs, while being influenced by process parameters, which should be considered in characterisation methods. The primary deformation modes of NCFs must be reasonably replicated in material models, while the selection of modelling scales relies on the balance of accuracy and efficiency, as well as issues of interest. Defects in preforms are typically of multiple scales and are related to process types. Effective methods for defect mitigation relies on deep understanding of the defect mechanisms. Finally, this paper outlines some future trends in the field, aiming to provide a reference for ongoing research on the manufacturing of NCF composites.