Co-design methods consist of jointly considering radar and communications systems when designing new systems to optimally share spectral resources. Such systems are jointly designed from scratch to efficiently utilize the spectrum and can potentially result in performance benefits when compared to an isolated approach to system design. Co-designed systems are not necessarily physically co-located. When operating from the same platform, co-design includes the cases where radar beams and waveforms are modulated to convey communications messages, an approach which is typically referred to as dual function radar communications systems. For example, some recent experimentally demonstrated co-design approaches include: