This study addresses the role of water vapour in Calcium Looping (CaL) cycles, and is based on results of an experimental campaign performed in a lab-scale fluidized bed reactor under operating conditions that are representative of a realistic CaL process. Tests have been designed so as to characterize the effect of steam in either the calcination or the carbonation stages, or in both. A reference limestone has been used, and its CO2 capture capacity, propensity to fragmentation and morphological and microstructural changes have been investigated upon iterated looping cycles. Results are discussed to highlight the role of steam on the course of calcium looping. (C) 2016 Elsevier B.V. All rights reserved.