Quantitative studies aiming at general explanations for the emergence of new political parties stress the importance of new issues and the programmatic behaviour of other parties. I connect these two aspects by arguing that the programmatic diversity of existing parties is a strong influence on the incentives for new party formation, as it determines the scope for possible programmatic innovations. I use two measures for programmatic diversity in order to capture the programmatic supply by existing parties. It can be shown that the explanatory contribution of programmatic factors is as high as or even higher than that of the factors usually cited in the literature on new political parties, e.g. electoral institutions. Moreover, the results underline the necessity of differentiating between genuinely new parties and splits from existing parties as subtypes of new political parties.