Quantitative Risk Management (QRM) often starts with a vector of oneperiod profit-and-loss random variables X = (X 1 , . . . , X d ) ′ defined on some probability space (Ω , F, P). Risk Aggregation concerns the study of the aggregate financial position Ψ (X), for some measurable function Ψ : R d → R. A risk measure ρ then maps Ψ (X) to ρ(Ψ(X)) ∈ R, to be interpreted as the regulatory capital needed to be able to hold the aggregate position Ψ (X) over a predetermined fixed time period. Risk Aggregation has often been studied within the framework when only the marginal distributions F 1 , . . . , F d of the individual risks X 1 , . . . , X d are available. Recently, especially in the management of operational risk, cases in which further dependence information is available have become relevant. We introduce a general mathematical framework which interpolates between marginal knowledge (F 1 , . . . , F d ) and full knowledge of F X , the distribution of X. We illustrate the basic issues through some pedagogic examples of actuarial and financial interest. In particular, we study Risk Aggregation under different mathematical set-ups, for different aggregating functionals Ψ and risk measures ρ, focusing on Value-at-Risk. We show how the theory of Mass Transportations and tools originally developed to solve so-called Monge-Kantorovich problems turn out to be useful in this context. Finally, we introduce some new numerical integration techniques which solve some open aggregation problems and raise new interesting research issues.