This paper discusses the need for professional change in approaches to tropical agriculture. The paper begins by recognising that on many past occasions, scientists have been wrong when they thought they were right. Recognition of these errors and limitations raises the question of the comparative advantages of our knowledge and farmers' knowledge: farmers undoubtedly know a lot that scientists do not. While scientists have an advantage in knowledge of pests, bacteria and viruses, farmers have an advantage with what can be perceived through continuous field observation and concerning the intricate relationships of their farming systems. The explanation of much of the failure of past technological transfer by scientists lies in the application of simplified and standardised approaches to complex, diverse and risk-prone conditions. The paper argues for a less reductionist approach to the complexity and diversity found, which requires that the appropriate experts are consulted: farmers. Farmer participation in the research process is therefore crucial. This in turn will require changes in attitudes, such that outsiders become catalysts and consultants, and farmers are enabled to undertake their own analysis. Visual representations are a key aspect of this. The paper ends with three questions: Whose knowledge counts? Who chooses? and Who gains? and with the recognition that transforming normal professionalism is the greatest challenge faced.