The demand for understanding the physical role of gangliosides in membranes is pressing, due to the high number of diverse and crucial biological functions in which they are involved, needing a unifying thread. To this purpose, model systems including gangliosides have been subject of extensive structural studies. Although showing different levels of complication, all models share the need for simplicity, in order to allow for physico-chemical clarity, so they keep far from the extreme complexity of the true biological systems. Nonetheless, as widely agreed, they provide a basic hint on the structural contribution specific molecules can pay to the complex aggregate. This topic we address in the present review. Gangliosides are likely to play their physical role through metamorphism, cooperativity and demixing, that is, they tend to segregate and identify regions where they can dictate and modulate the geometry and the topology of the structure, and its mechanical properties. Strong three-dimensional organisation and cooperativity are exploited to scale up the local arrangement hierarchically from the nano- to the mesoscale, influencing the overall morphology of the structure.