Ubicomp/HCI researchers are increasingly using smartphones to collect human-labelled data 'in the wild'. While this allows for the collection of a wide range of interesting data in authentic settings and surroundings, humans are notoriously inconsistent in the quality of their contributions. Improving the quality of data collected with mobile devices is a largely unexplored, but highly relevant field. The primary objective of this workshop is to share insights, ideas, and discoveries on the quality of mobile human contributions. The work presented in the International Workshop on Mobile Human Contributions (MHC '18) explores methods, tools, and novel approaches towards increasing the reliability of human data submissions with mobile devices.