TRELLIS provides an interactive environment that allows users to add their observations, opinions, and conclusions as they analyze information by making semantic annotations about on-line documents. TRELLIS includes a vocabulary and markup language for semantic annotations of decisions and tradeoffs, and allows users to extend this vocabulary with domain specific terms or constructs that are useful to their particular task. To date, we have used TRELLIS with a variety of scenarios to annotate tradeoffs and decisions (e.g., military planning), organize materials (e.g., search results), analyze disagreements and controversies on a topic (e.g., intelligence analysis), and handle incomplete and conflicting information (e.g., genealogy research).