In this document we extend and join Adaptive Structuration Theory with Task Technology Fit Theory and apply it to a health information technology setting. In our model, Human/Technology Adaptation Fit (HTAF) Theory, we assess the interactions between individual users and health information technologies. We develop HTAF, a model that focuses on the intersection of user adaptation and technology adaptation under the contexts of voluntary or mandatory health information technology, which both scholars and practitioners can use to determine the effects of the implementation of new technologies.