Agile method use in information systems development (ISD) has grown dramatically in recent years. The emergence of these alternative approaches was very much industry-led at the outset, and while agile method research is growing, the vast majority of these studies are descriptive and often lack a strong theoretical and conceptual base. Insights from innovation adoption research can provide a new perspective on analysing agile method use. This paper is based on an exploratory study of the application of the innovation assimilation stages to understand the use of agile practices, focusing in particular on the later stages of assimilation, namely acceptance, routinisation and infusion. Four case studies were conducted, and based on the case study findings, the concepts of acceptance, routinisation and infusion were adapted and applied to agile software development. These adapted concepts were used to glean interesting insights into agile practice use. For example, it was shown that the period of use of agile practices does not have a proportional effect on their assimilation depths. We also reflected on the sequential assumption underlying the assimilation stages, showing that adopting teams do not always move through the assimilation stages in a linear manner.