Traditional interfaces are continuously being replaced by mobile, wearable, or pervasive interfaces. Yet when it comes to the input and output modalities enabling our interactions, we have yet to fully embrace some of the most natural forms of communication and information processing that humans possess: speech, language, gestures, thoughts. Very little HCI attention has been dedicated to designing and developing spoken language, acoustic-based, or multimodal interaction techniques, especially for mobile and wearable devices. In addition to the enormous, recent engineering progress in processing such modalities, there is now sufficient evidence that many real-life applications do not require 100% accuracy of processing multimodal input to be useful, particularly if such modalities complement each other. This multidisciplinary, one-day workshop will bring together interaction designers, usability researchers, and general HCI practitioners to analyze the opportunities and directions to take in designing more natural interactions especially with mobile and wearable devices, and to look at how we can leverage recent advances in speech, acoustic, and multimodal processing.