Information fusion aims at a synergistic exploitation of multiple information sources, to enable decision-making or to enhance its performance. The sources include sensors of various modalities and characteristics, as well as sources which are not sensors. We discuss the challenges of information fusion, technical directions and approaches that can cope with those challenges, and the opportunities those approaches enable. Several research and development efforts conducted at MIT Lincoln Laboratory over the recent years in the area of information fusion for chemical-biological defense serve as the backdrop for that discussion.