Despite the recent development of theories in the social sciences that define human development and functioning in an integrated, nuanced and complex manner, the social work concept of “person-in-environment” remains outdated and limited. This is in part due to the “person” and “environment”--the biological, psychological, and social environments--being defined in distinction from one another. In order to remain current and effective in arguing on behalf of a clear professional voice in the field, social workers must not only engender but also promote a fundamental practice perspective that addresses complexity. A reformulation of “person-in-environment” can help social workers more fully realize the desire to unite under the common professional mandates requiring that both a “person-in-environment” perspective and a full biopsychosocial picture be taken into clinical accounts. To meet this aim I develop the concept of contextual adaptation, a new definition of “person-in-environment” reliant on tenets of nonlinear dynamic systems theory, specifically chaos theory. Nonlinear dynamic systems theory offers a unique opportunity for social workers to retain the core potentiality and utility of “person-in-environment,” that which enables them to account for the importance of environment, but reformulate it so as to create a more viable concept. Contextual adaptation is defined as a biopsychosocial process allowing for an integrated focus on the influence and management of the overlapping contexts of self, interpersonal experience, and sociocultural demands. Human development and functioning are established as a spectrum of adaptive behavior based on the regulation of the needs and requirements of internal processes, relational experience, and external influence.