# system > A system is an interconnected set of elements that is coherently organized in a way that achieves something. > > – [[Thinking in Systems]] > If you look at that definition closely for a minute, you can see that a system must consist of three kinds of things: elements, interconnections, and a function or purpose. > > – [[Thinking in Systems]] > So what is a system? Simply a set of things that are interconnected in ways that produce distinct patterns of behaviour – be they cells in an organism, protestors in a crowd, birds in a flock, members of a family, or banks in a financial network. And it is the relationships between the individual parts – shaped by their [[stocks and flows]], [[feedbacks]], and delay – that give rise to their emergent behaviour > > – [[Doughnut Economics]] > - A system is more than the sum of its parts. > - Many of the interconnections in systems operate through the flow of information. > - The least obvious part of the system, its function or purpose, is often the most crucial determinant of the system’s behavior. > - System structure is the source of system behavior. System behavior reveals itself as a series of events over time. > > – [[Thinking in Systems]] > most of the challenges that really matter involve systems, for example, energy and global warming; water, food, and population; and health and social justice. > > – [[A Systems Literacy Manifesto]]