A Phenomenological model is proposed for the rates of bubble coalescence and bubble break-up in turbulent gas-liquid dispersions. Bubble coalescence is modeled by considering bubble collisions due to turbulence, buoyancy, and laminar shear, and by analysis of the coalescence efficiency of collisions. Bubble break-up is analyzed in terms of bubble interactions with turbulent eddies. A method for the measurement of coalescence and break-up events in turbulent systems is described and used to test the validity of the proposed model. The measurement technique relies on the mixing of tracer gases within bubbles upon coalescence, in conjunction with Monte-Carlo simulations of coalescence events. Both distilled water and salt solutions are examined. Favorable agreement is found between the model and the individual coalescence and breakage rates, as well as with data obtained for the average bubble size and bubble size distribution.