The literature finds that innovation studies are dynamic and pivot around the evolutionary economy, interactive models of innovation, systems of innovation and resources and capabilities based view. At the micro level, the resources and capabilities based view together with the perspective of the combination of internal and external resources help to determine the effect of the strategies of search of knowledge and the role of the absorptive capacity in the innovative performance. In the relationship between firms and their environment, specifically with the sources of external knowledge, the complementarity or substitution effect between internal and external resources is not duly confirmed. In the literature and in empirical studies, the results point in one direction (complementarity) or in another (substitution); versus this research gap, this thesis proposes to carry out a longitudinal study (most of the studies are cross-section), an analysis to see if the effect in Spanish companies tends towards complementarity -positive effect- or towards the substitution -negative effect- After an exhaustive collection of the evidence and literature on open innovation and absorptive capacity, we replicate existing models to provide strong and empirical analyzes with longitudinal data, evidence that justifies one effect or another. In the first model, the results suggest caution in the interpretation of external search strategies: breadth and depth. In the second model, the results indicate that the moderating role of the absorptive capacity produces a substitution effect, but also the existence of a process of accumulation of knowledge as antecedent of the absorptive capacity. The thesis is presented with three different but related lines of work that address the topic of firms' innovation, from a theoretical and empirical perspective. Consequently, the main contributions of the present work have been to confront and evidence, from the empirical point of view with longitudinal data, the theoretical approaches related to the strategies of search of external knowledge and the absorptive capacity.; La literatura constata que los estudios de innovacion son dinamicos y pivotan alrededor de la economia evolutiva, los modelos interactivos de innovacion, los sistemas de innovacion y la vision basada en los recursos y capacidades. A nivel micro, la vision de los recursos y capacidades junto con la perspectiva de la combinacion de recursos internos y externos ayudan a determinar el efecto de las estrategias de busqueda de conocimiento y el papel de la capacidad de absorcion en el resultado innovador. En la relacion entre las empresas con su entorno, especificamente con las fuentes de conocimiento externo, el efecto complementariedad o sustitucion entre los recursos internos y externos no se encuentra debidamente confirmado. En la literatura y en estudios empiricos, los resultados apuntan en una direccion (complementariedad) o en otra (sustitucion); ante este gap de investigacion, la presente tesis plantea realizar a traves de un…