The Colloquium is intended to review current advances on the dynamics of strongly coupled dispersed two-phase flows involving solid particles, droplets or bubbles in which particle-particle interactions or collective behaviors take place and modify the continuous flow field. Such situations typically arise in “laminar” two-phase flows (sedimenting suspensions, bubble columns... ), but also in turbulent conditions (dense fluidized beds, spray dispersion ...) where clustering or collective effects may affect the settling velocities and more generally the turbulent dispersion of the dispersed phase. Contributions will concern both key experiments (including DNS) shedding light on fundamental mechanisms (micro-structure, screening, turbulent dispersion, pseudo-turbulence, turbulence modulation, clustering, large-scale instability, gravity driven two-phase flows...). and the mathematical representation of these effects through refined averaged modeling with emphasis on closures. Some contributions dealing with applications and enlightning the modelling needs will be welcome.