Purpose: The paper identifies, outlines, and categorises establishment and operational factors that contribute to successful agricultural on-farm demonstration. Design/Methodology/approach: The paper is based on a literature review on demonstration activities and meta-analysis of 24 original case study reports from 12 European countries. Findings: Based on a combination of deductive and inductive analysis, the success determinants are classified into nine critical success factors deemed important in designing an on-farm demonstration event (the 'Nine Ps'): Purpose, Problem, Place, Personnel, Positioning, Programme, Process, Practicalities, Post-event engagement. Each factor ('what') is framed in terms of success principles to provide a guide to its enactment ('how'). Practical implications: The results of the analysis can serve as a practical decision-support tool for organisers and evaluators of on-farm demonstration events. Theoretical implications: The paper broadens the perspective on the character, interlinkages, and relative importance of the factors underlying demonstration and their successful application within the agricultural knowledge and innovation system. Originality/Value: The paper addresses the deficit of comprehensive empirical studies investigating on-farm demonstrations by offering a rich research-based analysis of the factors and principles underlying their successful implementation.