Over the last decade, the tremendous growth in the mobile Internet user population has been accompanied by an equally exciting evolution in wireless data networks. However, quite understandably, the evolution has been distinctly characterized by an increasing degree of heterogeneity along several dimensions such as the access technology, network model, device, and application requirements. This heterogeneity, in turn, imposes a significant challenge on the design of the network protocol stack, and leads to the question: how can the protocol stack at a mobile host cater effectively to the heterogeneous characteristics of the operating environment? In this article we provide an overview of AdaptNet, an adaptive protocol suite for next-generation wireless data networks. AdaptNet consists of protocol solutions at different layers of the protocol stack addressing several problems, including rate adaptation, congestion control, mobility support, and coding. A common underlying theme in the design of the protocols in the AdaptNet suite is adaptiveness to the operating environment. Through high-level discussions, preliminary results, and pointers to relevant related work, we show how AdaptNet achieves the goal of effectively addressing heterogeneity in next-generation wireless data networks.