This book contains papers invited after the First International Workshop on Mobile Social Signal Processing, MSSP 2010, held in Lisbon, Portugal, in September 2010. The 9 revised papers included in this volume represent the diversity of two fields of research, Mobile HCI and Social Signal Processing, and areas of overlap. They cover a wide range of topics spanning from approaches for effective interaction with mobile and wearable devices to modelling, analysis and synthesis of nonverbal behaviour in human-human and human-machine interactions.