Ecological and systems theories provide a framework for understanding the interplay between organisms and their environments, emphasizing reciprocal relationships and interdependence. Bronfenbrenner's ecological systems theory focuses on multiple layers of influence (micro, meso, macro, chronosystem) affecting development and well-being. In social work practice, these theories guide engagement, assessment, goal setting, intervention, and evaluation, highlighting the importance of understanding both the client and the systems around them.