Why do farmers adopt new practices? This thesis explores agricultural adoption. Drawing on prior research that has used economic, sociology and social psychology literature to describe and explain the social phenomenon of the adoption of a new technology. This thesis uses a mixed methods approach to examine grassland management and nutrient management practices by Irish dairy farmers. Understanding the adoption of these specific practices is important because of conflicting political and policy interests: the objective of increasing production, while simultaneously achieving sustainable farming. The research is organised into three separate studies making a number of distinct contributions. This work extends the current agricultural adoption literature by using literature and concepts, beyond agricultural economic theory, to explain the process of adoption. Specifically, the use of the evolutionary theory of the firm provides an alternative perspective to agricultural adoption. As such, this work provides a deeper explanation of the adoption process. The first study highlights the impact of mandatory adoption of practices through participation in agri-environmental schemes. Highlighting the ineffectiveness of mandatory schemes for innovation; it identifies the adoption-innovation gap. Second, the application of the Technology Acceptance Model in study two indicates the comparative strength of farmer perception, with variables more traditionally used in the agricultural adoption literature for predicting intention to use practice. It also identifies a social influence variable and groups of influential social actors. In terms of context, the thesis presents the first application of the TAM to a nationally representative sample of Irish farmers. The third study is one of a limited number of empirical applications of the organisational routines literature. It is to the knowledge of the author the first application in the dairy sector and the second in the agricultural sector internationally. It deepens the understanding of agricultural adoption by drawing on this literature specifically for land management practices in the dairy sector.