Categorical and graphical models of programming languages

Declaration I hereby declare that this thesis has not been submitted, either in the same or different form, to this or any other university for a degree. Acknowledgements First of all, I would like to thank my first supervisor, Alan Jeffrey, for his constant support, advice, and enthusiasm for my research. Many thanks to my second supervisors, Matthew Hennessy and Marcelo Fiore, for their encouragement and technical help in the final stages of my work, and for their comments on parts of the draft of the thesis. Thanks to Julian Rathke for sharing his experience, and for encouragement throughout my research, and for comments on parts of the draft. I would like to thank all past and present members of the Foundations of Computation group at Sussex University, for discussions and feedback. for their interest in my work, and helpful discussions. I would like to thank my parents for supporting me all through my student years, both financially and emotionally. And finally, many thanks go to Amanda, for her support in the finishing stages of the thesis; without her help, this thesis might not have been finished.