With the increasing constraints set by the European Commission to reduce Carbon dioxide and nitrogen oxide/dioxide emissions, the aerospace industry is attempting to combat this issue by increasing the utilisation of advanced composite materials. However, the transition from metal alloys to advanced composites on primary or secondary structures as well as propulsion jet engines does not come without its challenges, one of which is the impact performance of carbon fibre-epoxy composites. The aim of this work is to improve the impact performance of composite by developing novel, complex and sophisticated fibre architectures where the crack propagation within composite laminates is more difficult. This process is called interleaving and it is carried out using an automated deposition technique called Automated Fibre Placement (AFP). An AFP deposition head deposits strips of pre-impregnated carbon fibre-epoxy tapes and does so using independent feed and cut mechanisms. By selecting which tapes are active during the deposition process, it is possible to create an interleaved fibre architecture. As not all the available tapes are deposited by the AFP head in order to create an interleaved fibre architecture, the manufacturing performance is impacted with the simplest interleaved fibre architecture requiring double the deposition time (compared to a standard AFP laminate), while the most complex interleaved fibre architecture explored in the project requires quadruple the deposition time (compared to a standard AFP laminate). Within this thesis conventional Design Principles, Concepts, and Solutions are used to develop the Interleaved Laminates, and from these developments three levels of Interleaving are chosen for manufacturing and physio-mechanical assessment. Three different material types are used in order to evaluate any effects of material and processing properties on the interleaved laminates (structure versus property concerns); with more traditional AFP laminates produced and mechanically assessed in the same testing regime, to act as appropriate baselines for any performance evaluation. The Interleaved Laminates are evaluated in their Tensile, Compressive, Mode I Fracture Toughness, Mode II Fracture Toughness, Flexural and Combined Through thickness Compression/Shear properties, where all the levels of Interleaved laminates are compared to a standard AFP laminate. Unfortunately there was no impact testing completed within this study, as it was determined that to understand the changes in fundamental mechanical properties was more important at this stage, before moving forward to more complex failure modes such as high strain rate impact. From the analysis of the mechanical testing carried out, it was found that it is possible to obtain an improvement of 23.3% in Mode I Fracture Toughness and 34.9% in Mode II Fracture Toughness for a specific structural and material configuration. These improvements are achievable at the expense of Tensile properties of 9.8% for the Mode I Fracture Toughness improvements and 7.1% for the Mode II Fracture Toughness improvements. It is broadly concluded that for design cases where Mode I and Mode II Fracture Toughness are the limiting factor, interleaving is a suitable and beneficial alternative for conventional laminates. However, in design cases where tensile (and for some configurations compressive) properties are the limiting factor, Interleaving is not most suitable manufacturing method.