Huldrych Zwingli and Johannes Oecolampadius met with Martin Luther and Philipp Melanchthon in Marburg beginning October 1, 1529 till October 3. They agreed on 14 of 15 points but, as everyone knows, they couldn’t come to agreement on the meaning of the Lord’s Supper. Luther was far too ensconced in Roman Catholic theology to see with the clarity with which Zwingli saw. Consequently, Luther left the conference angry and Zwingli left depressed.
Philip Schaff does a nice job of summarizing both the discussions and the viewpoints of the major actors.