This thesis presents work done with wearable haptic devices for the purpose of enhancing human-machine interaction. Haptic devices capitalize on the unrealized potential of our body--and particularly our skin--to perceive stimuli by contact. To address the challenge of training motor skills, my first area of focus deals with the question of how best to provide guidance information for trajectory-following tasks. Results indicate that spatially-separated assistance rendered through a tactile device can be as effective for guidance as a the same information presented through a kinematic device. In addition to that, exploring the concept of communicating with a wearable haptic device, the remainder of this thesis focuses on a novel, multi-modal, wearable haptic device, MISSIVE, which is capable of rendering information-rich haptic cues. My experiments demonstrate that this approach can increase perceptual accuracy compared to a uni-modal vibrotactile system of comparable size and that users prefer the multi-modal device.