Social work is the professional application of social science research in an effort to improve the lives of people and promote various forms of social equality. Systems theory is an interdisciplinary field that studies complex systems. Social workers approach systems theory as a way of studying the different levels of society and understanding how component parts therein function in the whole. They then apply their findings to promote the betterment of society.
Social workers can function in a variety of capacities. They can be advocates, researchers, academics, policymakers, mental health professionals, administrators or even just casual volunteers. Generally, the thing that binds them is a concern for furthering the cause of social justice, as they seek to understand the causes and alleviate the effects of a variety of social problems.
Systems theory is the general name for a host of different methodologies and particular theories. All of these theories tend to assume that systems are holistic--some use the term "organic"--and that there is a causal interrelationship between the parts and the whole of any system. Systems theory in the social sciences tends to observe the reciprocal influence between social environments and the individuals therein.
Social workers employing social theory on the micro level are concerned with individuals, families and other small communities. Generally, mental health professionals and child safety advocates tend to work at this level. They are primarily concerned with the safety and welfare of individuals and with fostering positive and healthy dynamics within family relationships.
This level of social work tends to focus on small communities such as neighbourhoods or regions. Workers at this level tend to be members of local agencies or other small organisations seeking to help develop and advocate policies and programs designed to bring about social change on a local level.
Social workers at the macro level tend to be involved with policy formation and social research on a broad scope, focusing on whole societies or even working internationally. They tend to apply systems theory to understand how to better the conditions of people living within entire nations or on a global scale.