1: Conceptual Structures. 1. Introduction. 2. Overview. 3. Conceptual Graphs: What they Are and How they Work. 4. Previous Work in Constraints and Unification over Conceptual Graphs. 5. Summary. 2: Unification, Knowledge Structures and Constraints. 1. Introduction. 2. Unification. 3. Feature Structures. 4. Logic Programming, Constraint Logic Programming, and Constraint Satisfaction Problems. 5. Unification and Constraints. 6. Knowledge Structures, Partialness and Unification. 7. Summary. 3: An Algorithm for the Unification of Conceptual Graphs with Constraints. 1. Introduction. 2. Interval Constraints. 3.Projection and Constraints Using Intervals. 4. Unification over Constraints. 5. Unification Algorithm. 6. Summary. 4: Results, Demonstrations and Comparisons. 1. Introduction. 2. Design. 3.Experiments: Simple Structures. 5. Comparisons to Other Systems. 6. Summary. 5: Placing the Unification Model in Context. I. Introduction. 2. A Framework of Unification Methods. 3. A Toolbox for Knowledge Conjunction on Conceptual Graphs. 4. Extending the Model. 5. Summary. 6: Conclusions and Further Work. 1. Conclusions. 2. Future Directions.