In this dissertation I test the hypothesis on the origin of presidentialized parties that appear as the specific historical and empirical model of party organization. The model of presidentialized parties does not represent the next phase in the existing developmental theory of political parties, which would indicate movement towards another new type of party organization, nor can it be attributed with the meaning and value of a new developmental type. It is valid only as an analytical model which follows the adaptation of modern political parties to the challenges of social and political factors for the increasing individualization of political life on the historical and empirical level. What makes presidentialized parties a specific model are the key characteristics of the strong concentration of power in the hands of party leader and the centralization of decision-making process, from which derive his autonomy in the formulation of party policies, programs and electoral strategies, unquestioned supremacy over all levels of the party organization and the rigid hierarchical party structure. A comparative analysis of the British Labour party, the Spanish socialist worker's party and the Croatian democratic union unambiguously confirmed the main hypothesis which established a causal relationship between the complex combination of structural and contextual factors that are identified as the main drivers of the process of presidentialization, on one hand, and the emergence of the presidentialized parties which organizationally adapt to the challenges of modern democracies, on the other. In this dissertation I test the hypothesis on the origin of presidentialized parties that appear as the specific historical and empirical model of party organization. The model of presidentialized parties does not represent the next phase in the existing developmental theory of political parties, which would indicate movement towards another new type of party organization, nor can it be attributed with the meaning and value of a new developmental type. It is valid only as an analytical model which follows the adaptation of modern political parties to the challenges of social and political factors for the increasing individualization of political life on the historical and empirical level. What makes presidentialized parties a specific model are the key characteristics of the strong concentration of power in the hands of party leader and the centralization of decision-making process, from which derive his autonomy in the formulation of party policies, programs and electoral strategies, unquestioned supremacy over all levels of the party organization and the rigid hierarchical party structure. A comparative analysis of the British Labour party, the Spanish socialist worker's party and the Croatian democratic union unambiguously confirmed the main hypothesis which established a causal relationship between the complex combination of structural and contextual factors that are identified as the main drivers of the process of presidentialization, on one hand, and the emergence of the presidentialized parties which organizationally adapt to the challenges of modern democracies, on the other.