The majority of Brazilian industrial companies operating in the agricultural machinery sector use an informal product development process. This is most apparent in small and medium sized companies, whose products are usually developed based on adaptations of existing, previously commercialized, solutions. This paper proposes a Reference Model for the Agricultural Machinery Development Process (RM-AMDP), designed to clarify the existing knowledge of this process, thereby shedding light on and formalizing this practice. The reference model comprises the phases of project planning, product design and manufacturing planning, pilot production, product launch on the market, validation of agricultural machinery and project closure. Each of these phases is composed of activities for which the input data required for their execution and their deliverables are modeled. Three other dimensions of the process are also detailed: the knowledge domain, the mechanisms used and the controls. This model can be applied for teaching engineering students and as a basis for companies to improve their product development processes.