The purpose of the present study is to provide a critical review on the revolution of the "compliance" concepts from compliance to adherence, and adherence to concordance for both pharmacological and non-pharmacological therapies. A comprehensive literature search was performed using online databases from Library of University Putra Malaysia, and Pub Med based on the keywords. The present study showed that both quantitative and qualitative studies cannot be neglected in assessing adherence and its related problems. One of major findings from the present review is that "compliance" was no longer suitable for current treatments and it is important to define concepts of the terms used (adherence or concordance) correctly and clearly. The findings reflected that researchers placed greater value on medication adherence than non-pharmacological adherence. There were three general factors related to treatments adherence, namely socio-economic factor, treatments-related factor and disease-related factor. The findings showed that both qualitative and quantitative studies found consistent results for most of the factors, except for the experience of diseases symptoms. Both study design contribute important values to the adherence studies and future studies should incorporate both quantitative and qualitative studies to understand adherence in both pharmacological and non-pharmacological treatments.