Heterogeneity and convergence are two distinctive connotations of future wireless networks emanated from International Telecommunications Union (ITU)’s vision of Optimally Connected, Anywhere, Anytime. Multiple access networks, multiple terminals and multiple services are expected to converge in a manner where heterogeneity can be exploited to realize this ultimate goal. This raises the importance of radio resource management (RRM) for a multiple radio access technologies (multi-RAT) environment, where coalitions of heterogeneous access networks are each connected to a common Internet Protocol (IP)-based core network. In this article, we develop a cooperative RRM framework for future IP-based multi-RAT environment to coordinate better utilization of radio resources in an opportunistic yet altruistic manner. We motivate the importance of cooperation which can exploit heterogeneity as an enabler to improve system capacity and quality of service (QoS) of users. We exemplify the proof of concept based on a heterogeneous multiple access points (multi-AP) wireless local area network (WLAN) and argue that our technology agnostic approach is readily applicable to future IP-based multi-RAT environment. We demonstrate that our cooperative RRM framework benefits from the unified actions of joint optimization and results in a QoS-balanced system by enabling different functional entities to form synergies and multiple access networks to interact. We further show that a QoS-balanced system has salient traits of providing statistical QoS guarantee to support demanding multimedia applications while maximizing overall system capacity. Consequently, we advocate the notion of QoS balancing as criterion to quantify the state of balance in future IP-based multi-RAT environment.