The increasing demands for more durable, lighter, and smarter structures have led to the development of new and advanced composites. Increased strength and simultaneous weight reduction have resulted in energy savings and applications in several manufacturing industries, such as the automotive and aerospace industries as well as in the production of everyday products. Their optimal design and utilization are a process, which requires their characterization and efficient modeling. The papers published in this Special Issue of the Journal of Composites Science will give composite engineers and scientists insight into what the existing challenges are in the characterization and modeling for the composites field, and how these challenges are being addressed by the research community. The papers present a balance between academic and industrial research, and clearly reflect the collaborative work that exists between the two communities, in a joint effort to solve the existing problems.