The document summarizes Nathan Schneider's presentation on preposition semantics. It discusses challenges in annotating prepositions in corpora and approaches to their semantic description and disambiguation. It presents Schneider's work on developing a unified semantic scheme for prepositions and possessives consisting of 50 semantic classes applied to a corpus of English web reviews. Inter-annotator agreement for the new corpus was 78%. Models for preposition disambiguation were evaluated, with the feature-rich linear model achieving the highest accuracy of 80%.