In this article, we describe the generation of a Design and Implementation Framework for Mathematical Modelling Tasks (DIFMT) through a researcher-teacher collaboration. The purpose of the framework is to support holistic approaches to instructional modelling competency. This framework is underpinned by principles drawn from theory and praxis which are informed by the anticipatory capabilities that teachers require for the design and effective implementation of quality modelling tasks in secondary classrooms. A draft DIFMT was developed from a synthesis of research literature and was refined through an iterative process of task development, implementation and observation, reflection through teacher/student interviews, and revision of the framework. Each iteration made use of the most recent refinement of the co-constructed DIFMT, building theory while simultaneously addressing a problem in educational practice, consistent with a design-based methodology. Thus, the DIMFT developed organically throughout the project. While initial modelling exemplars were researcher-designed, the locus of responsibility moved to teachers as the project progressed. The DIFMT consists of two major components--principles for modelling task design and pedagogical architecture--each of which is structured around dimensions that include elaborations which detail the knowledge required for modelling as well as teacher and student capabilities.