This thesis is a study of the oaths sworn by subjects to kings of England between c. 870 and c. 1200. Who swore oaths to the king? When did they swear? What sorts of oaths were sworn? What commitments did swearing lead to? Where were oaths sworn, and what rituals were involved in swearing? These are some of the questions asked of the evidence, a combination of narrative and legal sources. This material is examined over four thematic chapters. The first three look at oaths sworn ordinarily at the time of accessions, as part of succession planning, and within the confines of reigns themselves, respectively. The final chapter examines oaths sworn outside of this process—oaths sworn in non-normal, extraordinary circumstances.