We discussed existing, mainly supply-side, theories of the TNC. We pointed out various deficiencies and tried to rectify this by building on developments on the Penrosean perspective. We moved on to suggest the elements of a synthesis of supply-side theories, to account for (endogenous) growth, motivation, direction of expansion, and choice of institutional mode. We observed the lack of consideration for demand-side issues in the theory of international production and the TNC, and went on to suggest that demand-side considerations can be an additional reason for geographical diversification, leading to a genuine ‘all-weather company’. We suggested that a synthesis of supply-side considerations can explain the choice of institutional mode, when carefully applied in specific cases of specific firms. Last, but not least, we have suggested that the only generalization from the literature and our analysis is that one cannot generalize. All theories can be of use in certain cases, but no theory in all cases and all of the time. This applies equally to the demand-side arguments we have suggested in this chapter.