Elinor Ostrom pointed out significance of rule structures, and the need for institutional diversity in addressing commons problems.This is particularly true in relation to the governance of large-scale commons resources and one global commons that requires attention is the economic system.We share the institutional arrangements that generate economic benefits but neither the wealth generated by the system, nor the negative impacts, are shared equally.The result is an economic system focused on the privatisation of shared resources that generates inequalities around the globe. This paper explores the economic system as a ‘co-created’ commons.The paper brings together two broad strands of literature on commons: one arising from the public trust doctrine, and the other based on the economic characteristics of a good or service in terms of its access (‘excludability’) and consumption (‘subtractability’).The paper links these concepts with more recent work on ‘productive commons’, where shared resources are generated through collaborative activity, and ideas from evolutionary economics, which explore the economic system as a process and structure of rules, rather than as a series of transactions based on the allocation of property rights.Evidence is provided to support the argument that commons are an integral element of the economic system, and as a result account for some of its efficiencies and, where rule structures fail, for negative impacts on socio-economic and ecological systems.

In this chapter, we discuss problems in the single-stage or parallel-units environment. The problem statement is presented in Section 4.1. Three types of models are presented in Section 4.2 (sequence-based), Section 4.3 (continuous time grid-based), and Section 4.4 (discrete time grid-based). In Section 4.5, we present how batching decisions can be handled, and in Section 4.6 we discuss how the three types of models can be extended to handle a new feature, namely, general shared resources. Finally, in Section 4.7 we present extensions on the modeling of general resource constraints using discrete modeling of time. Building upon the material in Chapter 3, we illustrate how some of the modeling techniques introduced for single-unit problems can be extended to account for multiple units. Our goal is to outline some general ideas that the reader can apply to a wider range of problems.We focus on (1) problem features that are new, compared to the ones in single-unit problems (i.e., batching decisions and general shared resources); and (2) new modeling techniques that are necessary to account for these features.