30 It can be said, with a sense of lively gratitude to the Spirit of Truth, that the Second Vatican Council was a blessed time, during which the bases for the Catholic Church's participation in ecumenical dialogue were laid. At the same time, the presence of many observers from various Churches and Ecclesial Communities, their deep involvement in the events of the Council, the many meetings and the common prayer which the Council made possible, also helped bring about the conditions for dialogue with one another . During the Council, the representatives of other Churches and Ecclesial Communities experienced the readiness of the worldwide Catholic Episcopate, and in particular of the Apostolic See, to engage in dialogue.
Source: Ut Unum Sint (Vatican.va)