This edited volume with selected expanded papers from CELDA (Cognition and Exploratory Learning in the Digital Age) 2011 (http://www.celda- -conf.org/) will focus on Ubiquitous and Mobile Informal and Formal Learning in the Digital Age, with sub-topics: Mobile and Ubiquitous Informal and Formal Learning Environments (Part I), Social Web Technologies for new knowledge representation, retrieval, creation and sharing in Informal and Formal Educational Settings (Part II), Virtual Worlds and Game- -based Informal and Formal Learning (Part III), Location- -based and Context- - Aware Environments for Formal and Informal Learning Integration (Part IV) There will be approximately twenty chapters selected for this edited volume from among peer- -reviewed papers presented at the CELDA (Cognition and Exploratory Learning in the Digital Age) 2011 Conference in Rio de Janeiro, Brazil in November, 2011.