We consider the provision of access point buffers in WLANs. We first demonstrate that the default use of static buffers in WLANs leads to either undesirable channel under-utilisation or unnecessary high delays, which motivates the use of dynamic buffer sizing. Although adaptive algorithms have been proposed for wired Internet, a number of fundamental new issues arise in WLANs which necessitates new algorithms to be designed. These new issues include the fact that channel bandwidth is time-varying, the mean service rate is dependent on the level of channel contention, and packet inter-service times vary stochastically due to the random nature of CSMA/CA operation. We propose an adaptive sizing algorithms which is demonstrated to be able to maintain high throughput efficiency whilst achieving low delay.