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As mobile nodes roam in a wireless network, they continuously associate with different access points and perform handoff operations. However, frequent handoffs can potentially incur unacceptable delays and even interruptions for interactive applications. To alleviate these negative impacts, we present novel association control algorithms that can minimize the frequency of handoffs occurred to mobile devices. Specifically, we show that a greedy LookAhead algorithm is optimal in the offline setting, where the user's future mobility is known. Inspired by such optimality, we further propose two online algorithms, namely LookBack and Track, that operate without any future mobility information. Instead, they seek to predict the lifetime of an association using randomization and statistical approaches, respectively. We evaluate the performance of these algorithms using both analysis and trace-driven simulations. The results show that the simple LookBack algorithm has surprisingly a competitive ratio .of (log k + 2), where k is the maximum number of APs that a user can hear at any time, and the Track algorithm can achieve near-optimal performance in practical scenarios.