Synopsis (short abstract)The study reflects on previous World Bank and FAO reports that made the general recommendation to set both research and extension investment targets in developing countries at 1% of agricultural gross domestic product (AgGDP). In order to define proxies for country-specific extension investment targets, authors developed an extension investment model (EIM) based on socio-economic macro-indicators (poverty, undernourishment, access to information and population density) and a method to define est imates for cost increases related to climate change. These parameters helped estimating the demand for agricultural extension and investments required for it. Results showed that about half of the 94 developing and emerging countries should spend more than 1% of their respective share of GDP derived from agriculture and about a quarter of the countries, mostly in Africa and South East Asia, need to spend more than 2% of their AgGDP. The paper reveals significant differences in average investment requirements in different regions and shows the additional extension costs related to climate change and other areas that currently lack investment.