The properties of a composite material are determined not only by the constitutive properties of the matrix and the reinforcement, but also by the type and nature of interfacial bonding between them. For thermo-mechanical applications, the influence of interfaces and interphases is fundamental. In this work, we comprehensively study the copper alloy/carbon fiber composite material interfaces, with and without interphases, in terms of microstructural and chemical properties at the micro- and nanometric scales. These properties are then correlated with the local mechanical properties as determined by nanoindentation, enabling us to establish a direct relationship between the chemistry and mechanical properties at the microscale. In addition to experimental measurements, three-dimensional finite element simulations are performed on the matrix/interphase/reinforcement system, and the results between experiments and simulations show very good agreement, validating our basic hypothesis that the local mechanical properties are determined by the material chemistry.