What document lists details of a media buy and establishes contractual obligations?

The correct answer focuses on the Insertion Order (IO), which is a crucial document in the media buying process. An Insertion Order serves as a formal agreement between the buyer and the media seller. It outlines detailed information regarding the advertising campaign, including specifics like the ad placement, schedule, pricing, and various terms and conditions related to the media buy. This document acts as a binding contract that establishes the obligations of both parties, ensuring that they adhere to the agreed terms.

In contrast, a Master Service Agreement (MSA) typically governs the overall relationship between parties and may cover various services beyond just a single media buy, making it broader and less focused on specific transaction details. A Request for Proposal (RFP) is used to solicit bids from potential vendors and does not itself represent an agreement or commitment. Similarly, a proposal is a document presented to outline potential solutions or plans but does not create any binding obligations like the Insertion Order does.