GEMINI-E3 is a multi-country, multi-sector, recursive computable general equilibrium model comparable to the other CGE models (EPPA, ENV-Linkage, etc.) built and implemented by other modeling teams and institutions, and sharing the same long experience in the design of this class of economic models. GEMINI-E3 has been extensively used in various European and national research projects and contracts to derive total costs and benefits of energy and climate policies. In some of these projects, several attempts were conducted to link GEMINI-E3 with Bottom-Up models (TIAM-WORLD, Swiss MARKAL, ETEM-Swiss). Various couplings were performed through harmonization of common exogenous parameters, exchange of variables, integration within GEMINI-E3 of a technological representation based on Bottom-Up model, calibration of CGE equations to inputs coming from the Bottom-Up model. This contribution aims at summarizing the various couplings that have been performed and tries to stress the main teachings of these experiments.