Current middlebox management mechanisms are clumsy and unsuitable for taking full advantage of new MB deployment models and diverse middlebox functionality. Instead, we advocate for mechanisms that help exercise unified control over the key factors influencing middlebox operations. Our goal is to realize a software-defined middlebox networking framework to simplify management of complex, diverse functionalities and engender rich deployments. In this talk, I will discuss the major challenges that arise---representing, manipulating, and knowledgeably controlling MB state---and the potential interfaces and abstractions for addressing them.