Textile materials differ in numerous aspects from conventional engineering materials. They are inhomogeneous, highly anisotropic and deformable, and can suffer large deformations and displacements within a plane at low stress under ordinary conditions and/or during normal use. Knowing their behaviour under low stress is the basis for the engineering planning of fabrics, product development, computer-aided design, and the numerical modelling and simulation of clothing and other products for technical applications. This monograph is aimed at providing a critical appreciation of scientific understanding in those areas related to complex deformations of textile structures. These contents are subdivided into two thematically-connected parts. Part I addresses the basic issues regarding the complex deformations of a textile structure and the simulation of drape performances, whilst Part II places emphasis on the 3D modelling of the human body, and clothing simulation. This monograph that builds practical, professional and academic foundations for tomorrow’s engineers will be an essential reference for academics, professionals, students, researchers, and designers within industry.