Activity-dependent long-term changes in synaptic efficacy are thought to be important in learning, memory formation, neuronal development and pathological states of neuronal excitability in the CNS. For the past two decades, numerous studies have investigated long-term changes in synaptic efficacy at excitatory glutamatergic synapses. Although inhibitory synapses are essential for proper functioning of the neuronal network, attention has focused only recently on describing and characterizing plasticity at these types of synapse. Not surprisingly, different forms of plasticity at GABAergic, and the closely related glycinergic, synapses have been reported in several regions of the brain. Here we review these different forms of plasticity and focus on their possible roles in developing and adult neuronal networks.