Stafford Beer’s Viable System Model is one of the most widely used Systemic approaches to management. It offers a robust theory on organisational viability and associated methodologies which supports the practitioner to map the warts-and-all reality of the way an organisation works, and then assess it with VSM criteria. It models an organisation as a neural network, where each node is itself an autonomous, viable system, and all nodes together constitute a purposeful and cohesive organisation. It has been applied at all scales from small work-groups to Small and Medium Enterprises, Corporations, communities and nation states, and experienced practitioners often tell of the power and speed of the model to identify and solve issues threatening organisational effectiveness. This chapter explains the basic VSM theory, a well-developed methodology to apply it for guided organisational self transformation, and a recent example of application in a Mexican service company, which resulted in very good improvements in key performance indicators. It offers a final reflection on innovative developments of the original theory in areas like governance, sustainability, industrial ecology and network management.