The Software Defined Network (SDN) is an established network paradigm, architecture and principles, that attracted significant research effort in recent years. An SDN-enabled infrastructure decouples network control from forwarding and enables direct programming. Recently, there is an increasing effort to introduce SDN support in the transport layers of the network operators WAN infrastructure, like Layer 0 (WDM & DWDM) and Layer 1 (SONET/SDH & OTN) technologies. We refer to this infrastructure as the “Software Defined Transport Network”, and benefits include network management devolvement, timely connectivity provision, improved scalability, and open and flexible programmability using well-defined API. This paper outlines the main elements of Software Defined Transport Networks and highlights relevant Application-Based Network Operations (ABNO) enabling technologies. We demonstrate how this technology will benefit network operators, and provide an overview of research results and deployment examples. Finally, we identify some of the technology gaps and future research opportunities.