The primary objective of this study is to explore the validity and applicability of two competing internationalisation theories; namely the 'Stage' theories and the New Venture Internationalisation (NVI) framework. The study concentrates on small to medium enterprises (SMEs) in the Irish software industry because these firms are highly dependent on exports and internationalisation to grow and survive, given the small size of the domestic market. The paper begins with a broad discussion on SMEs and on SME internationalisation. A background to the Irish software industry, with particular focus on indigenous software SMEs, which are achieving rapid growth within a dynamic global industry, is provided. The aforementioned frameworks of the internationalisation process of SMEs are comprehensively reviewed. Primary research, in the form of self-administered mail survey questionnaires, is employed to test the stated hypotheses. The survey findings indicate that Irish indigenous SMEs pursue pro-active internationalisation strategies, and internationalise at, or soon after inception. Moreover, international market selection decisions are primarily influenced by growth opportunities in those markets. Overall, these SMEs internationalise rapidly, and reach a high degree of international involvement within a relatively short space of time. It is concluded that the stage theories of internationalisation do not adequately describe and explain the international behaviour of Irish indigenous software SMEs. Indeed, the latter appear to be part of the 'Born Global' phenomenon, and conform to many aspects of the NVI framework.