Rapp will create a number of global campaigns that aim to generate sales meetings with identified prospects across a range of sectors.
The agency will develop two levels of activity, with one set of campaigns aimed at developing the company's overall global prospect database, and the others aiming more specifically at investors deemed to be in the top 10 per cent of SDI's global prospects.
SDI's main role is to attract investors into Scotland, and also to help Scottish companies break into international markets. In the past year, the group has assisted more than 700 Scottish organisations to do business internationally.
Rebecca Heaney, the Rapp managing partner, said: "Working with SDI is exciting because it not only allows us to create some really memorable work, but also gives us a role in helping the Scottish economy. We're very much looking forward to helping SDI achieve its goals."