Doctoral Thesis A Semantic Deconstruction of Session Types by Alceste Scalas This work investigates the semantic foundations of binary session types, by revisiting First and foremost, I wish to thank my PhD supervisor, Massimo Bartoletti, for his invaluable advice, for the long discussions in front of the whiteboard, and for all the opportunities he gave me to learn new things. The last 3 years have been intense and stimulating, and they certainly represent a pivoting point of my life-both professionally and personally. Massimo's role and influence is difficult to overstate. I also wish to thank Roberto Zunino: our looong Skype meetings have been a fundamental part of my PhD activity, and they have had a huge impact on my work. I am grateful to Simon Gay and Luca Padovani, for reviewing this thesis and giving detailed remarks and helpful suggestions. Thanks to Emilio Tuosto and Nobuko Yoshida for having me as a visiting student at their respective institutions, and for the insightful discussions and fruitful collaboration. During such visits, I also had the opportunity to work with Julien Lange: I am glad that this happened not just once, but twice! Thanks to my (ex-)colleagues at the University of Cagliari-in particular, Giovanni Casu,