This thesis reflects the results of action-research carried out in development cooperation, policy development and diplomacy. Research was conducted in three communities in Bolivia as well as in the offices of development practitioners, policy makers and diplomats. The research focuses on international cooperation in practice and as a practice. In this thesis I share my insights on how strategies, approaches and policies affect and shape international cooperation. In practice, development practitioners tend to shape their practices as interventions in order to fix the recipient’s problems through transfers. They shape the so-called beneficiaries’ social, discursive, political and performative practices. They assume policies will guide their actions through straightforward implementation. This might work very efficiently and effectively in rather simple situations in which entities (singular things or phenomena) and relations are separable, processes are linear and causality is easily understood. Both this interventionist type of development cooperation and simple situations are characterized by assumptions regarding high levels of differentiation, segmentation, predictability and stability. If the situation becomes complex rather than simple, which is often the case in development cooperation, then entities are still separable but relations have become inseparable (one relation affects other relations). And processes have become non-linear (feedback loops). I argue that in such a complex situation, development cooperation can best be shaped by the facilitation strategy and the fit-in-context approach. And it is better to understand policies as not being transferred through intermediaries but as being translated through mediators during implementation. To understand how ‘shaping’ takes place in such complex situations, the Actor-oriented approach and Actor-Network Theory are a useful frameworks. In my field research I noted that besides being complex, the reality I encountered can be fluid. This occurs when even the entities are inseparable, unstable, undifferentiated, volatile, turbulent or undetermined. I will give four examples. First, the Yuracaré corregimientos. These are territorial subdivisions. My research revealed that near the river they are demarcated by clear points and lines and that inside the forest their boundaries is blurred. So their nature is partly bounded and neat as well as partly amorphous and fused. The second example is about a sawmill. The sawmill the Yuracaré received from a development organization, has multiple, sticky imprints. These make its boundary blurred. Its nature is not a material singularity (one machine) but a socio-material assemblage of materialities and embodied knowledges, meanings, etc. Its sticky, blurred nature makes it inseparable from its earlier context. The third example is about inseparable policy issues. My research revealed that traide is an emerging policy assemblage which merges aid and trade and dissolves the traditional dividing line between those policy fields or practices. Finally, the example of Earth-beings. These are unknowns rather than determined entities. These various rather undifferentiated ‘objects’ that I encountered in my research, are causes for failure and surprise. They escape the common practice and notions used in international cooperation. Therefore, I propose different concepts to analyse them: becomings rather than beings and multities rather than entities. These becomings and multities render the situation fluid rather than complex. This poses challenges for development cooperation, policy development and diplomacy in practice. Instead of intervention or facilitation I argue there is a need to encourage self-development and to not be afraid to let-go. This strategy requires a different set of social, discursive, political and performative practices. Instead of the ‘fix-their-problems’ or ‘fit-in-context’ approaches, this research shows a need for a ‘go-with-the-flow approach’. Instead of controlling or mediating the policy cycle, there is a need to give space for creative reassembling. In these ways fluidity affects international cooperation as practice. Becomings and multities reveal a viscous reality of different differences. The entities constitute a topographic, solid space-time of points (positions), lines (relations, transitions), figures, extensions, phases, calculations and external references. The multities constitute a topological, fluid space-time of vectors, manifolds, intensities, flows (transformations), escapes and self-references. The solid and fluid are not separable but co-constituted and form an immanent viscous entirety. In this thesis, the viscosity does not refer to the nature or physicality of materiality but viscosity refers to the nature of realities, that is to see, it is ontological. Realities of different natures are enfolding in a continuous movement in-between becoming-a-being (stabilizing, differentiating) and being-a-becoming (destabilizing, deterritorializing). In such dynamic realities, development is not an externally aided or imposed transition from A to B but is always self-development of a partly amorphous assemblage. Development as a becoming is a transformation and movement in-between A and B (solid and fluid). Development cooperation is neither shaped by transfers nor actor-networking but by the continuous practices of assembling in the midst of processes of de- and reterritorialization. And policy development is not a cyclical process in time (where formulation is followed by implementation) but a movement in space-time, with stabilizing forces and escapes affecting the assemblages (see Chapter 6). As part of working in and studying international cooperation I also engaged with the practice of diplomacy (see Chapter 7). My research focuses on the changing bilateral relationship between the Netherlands and Bolivia. Both governments explored and desired a relation among equals. Equality was to be found in mutually beneficial geo-economic cooperation. In the new bilateral relationship, the lithium deposits in Bolivia became central, but the nature of lithium was differently perceived. Lithium can be conceived of as a passive natural resource out there. It is a chemical, inert substance placed in the periodic table of the elements. However, in Andean ontologies, lithium is an animated matter, an Earth-being. Through Andean practice, lithium is enacted as being alive and it must be taken care of. These different natures of lithium were negotiated in the diplomatic encounter I studied. What was foreign to politics (the natures of nature) has become part of foreign politics. This ontological politics is a transformative force for diplomacy as a practice. Diplomacy, seen as the art of overcoming incommensurable differences, is no longer merely a geopolitical or geo-economic affair but it became an ontological affair. It is needed to address peacefully the different ways of shaping, thinking and enacting worlds. The world is not only prior to practice (in terms of acting and performing) but a practice is prior to the world. The performativity of practice is enacting the world. Diplomats then become creative world-makers. Through a different practice, people bring different and multiple worlds into being. These multiple worlds can have different natures. I argue there is a need for acknowledging the different natures of the natural and of the human. The political nature of negotiating and enacting (often implicitly) different ontologies has to be acknowledged and should become part of diplomacy. The significance of this particular diplomatic practice no longer lies in the negotiation of incommensurable political positions but in negotiating incommensurable ontologies and worlds. In turbulent times, diplomacy is needed more than ever but simultaneously in need of transformation and expansion. Finally, diplomatic skills are needed in social sciences to address certain biases towards the topographical, particularly in Actor-Network Theory. A Deleuzian complementation, focusing on the varying intensities of separability, differentiation, stability and determination, would bring in more symmetry between the topographical and topological.