The Core Competence of the Coorporation - Prahad and Hamel (1990)
Prahad and Hamel were the first people to suggest the core competence model for business strategy. They essentially argued that a company should concentrate on what it is that makes them best in class (your core competencies) and the bits they are not great at they should look to partner with externals to achieve this. This approach is really the start of Open Innovation as companies realise they can't do it all.
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