Philosophers have been attracted by the theory that an agreement consists of undertakings by the parties. But the theory faces objections from three sides: unconditional undertakings by both parties are insufficient for an agreement; if the parties give interconditional undertakings, both comply if neither does anything; and, if one party gives an unconditional undertaking and the other a conditional one, a condition of interdependence is breached. The options are to live with the breach, to produce an undertaking-based theory that avoids (...) the objections, or to analyse an agreement otherwise than in terms of undertakings. I consider each option and advocate the third: a better theory is that two people have an agreement where one makes an offer to the other that the other accepts. (shrink)