- With the increasing international focus on transboundary cooperation as a part of the Sustainable Development Goal (SDG) Framework, there is global recognition of transboundary water cooperation as a tool for improved governance and management of transboundary surface and groundwaters. Yet, there is not an agreed upon definition of transboundary water cooperation in the literature. Most measures of transboundary water cooperation focus on agreements, particularly the number of agreements or their content. However, this generally does not measure or capture how actors behave in a cooperative process, nor whether the behavior had the intended consequences or outcomes (Daoudy and Kistin 2008). Therefore, we need further research on measures of the quality and outcomes of cooperative processes. This dissertation addresses these gaps by achieving three goals. First, it identifies the strengths and weaknesses of the methodology for SDG Indicator 6.5.2. The SDG Indicator 6.5.2 aims to measure “the proportion of transboundary basin area with an operational arrangement for water cooperation” (UN-Water 2017). It does this by comparing the UN-Water methodology to two other variations for measuring transboundary water cooperation. The comparison of the results from the three methods illustrates the variability in what is considered transboundary water cooperation. The second goal is to develop a clear, consistent, and representative definition of transboundary water cooperation. This goal proved challenging in that a statement-style definition of transboundary water cooperation has many limitations. Notably, they are broad and non-specific, which makes them less applicable to the variety of forms cooperation can take in basins and aquifers. Therefore, I develop the Four Frames of Cooperation, which is a neutral modular framework for developing context-specific explanatory definitions of transboundary water cooperation in basins and aquifers. The Four Frames of Cooperation are legal, institutional, relational, and outcome. The Four Frames of Cooperation framework forms the foundation for the third goal of this dissertation, which is to define effective transboundary water cooperation and operationalize a method to evaluate the effectiveness of cooperative processes over internationally shared waters. Overall, effective cooperation emphasizes the relational and outcome frames of cooperation, while working towards equitability and sustainability, which is operationalized by the Weighted Model of Effective Cooperation. This model has three stages: parameters, assessment, and evaluation, and together, they present a context-specific model for evaluating the effectiveness of transboundary water cooperation. This model presents a first step in qualitatively evaluating the effectiveness of transboundary water cooperation. Together, the Four Frames of Cooperation and the Weighted Model of Effective Cooperation aim to improve the understanding of cooperation and encourage a detailed evaluation of the quality, success, and effectiveness of cooperative processes.