Goal models and contracts offer complementary approaches to requirement analysis. Goal modeling has been effectively used to capture designer’s intents and their hierarchical structure. Contracts emphasize modularity and formal representations of the interactions between system components. In this paper, we present CoGoMo (Contract-based Goal Modeling), a framework for systematic requirement analysis, which leverages a new formal model, termed contract-based goal tree, to represent goal models in terms of hierarchies of contracts. Based on this model, we propose algorithms that use contract operations and relations to check goal consistency and completeness, and support incremental and hierarchical refinement of goals from a library of goals. Model and algorithms are implemented in a tool which enables incremental formalization and refinement of goals from a web interface. We show the effectiveness of our approach on an illustrative example motivated by vehicle platooning.