Ecumenism

The ecumenical openness must be conducted according to the norms of the Church and you will exclude any tendency to religious syncretism. (Gd 9 b)

Unitatis Redintegratio (Decree on Ecumenism Vatican II)
Directory for the application of Principles and Norms on Ecumenism (Pontificium Consilium ad Christianorum Unitatem Fovendam)
Ut Unum Sint (On commitment to Ecumenism, Ioannes Paulus pp. II)
The Ecumenical dimension in the formation of those engaged in pastoral work (Pontificium Consilium ad Christianorum Unitatem Fovendam)
Address of his holiness of John Paul II at the Ecumenical meeting with the Protestant and Orthodox Hungarian communities (Calvinist Church of Debrecen, Sunday, 18 August 1991)
Vatican cardinal warns against syncretism in dialogue; Polish prelate speaks of Divine Mercy RE: Cardinal Jean-Louis Tauran, president of the Pontifical Council for Inter-religious Dialogue, warned that poorly-catechized Christians should not take part in inter-religious dialogue. “Christians, often ignorant of the content of their own faith and incapable because of this of living of and for it, are not capable of inter-religious dialogue that always begins with the assertion of one’s own convictions,” he cautioned. “There is no room for syncretism or relativism! Faced with adepts from other religions with a strong religious identity, it is necessary to present motivated and doctrinally equipped Christians.”
Sacraments (canon 844)

§1. Catholic ministers administer the sacraments licitly to Catholic members of the Christian faithful alone, who likewise receive them licitly from Catholic ministers alone, without prejudice to the prescripts of §§2, 3, and 4 of this canon, and can. 861, §2.
§2. Whenever necessity requires it or true spiritual advantage suggests it, and provided that danger of error or of indifferentism is avoided, the Christian faithful for whom it is physically or morally impossible to approach a Catholic minister are permitted to receive the sacraments of penance, Eucharist, and anointing of the sick from non-Catholic ministers in whose Churches these sacraments are valid.
§3. Catholic ministers administer the sacraments of penance, Eucharist, and anointing of the sick licitly to members of Eastern Churches which do not have full communion with the Catholic Church if they seek such on their own accord and are properly disposed. This is also valid for members of other Churches which in the judgment of the Apostolic See are in the same condition in regard to the sacraments as these Eastern Churches.
§4. If the danger of death is present or if, in the judgment of the diocesan bishop or conference of bishops, some other grave necessity urges it, Catholic ministers administer these same sacraments licitly also to other Christians not having full communion with the Catholic Church, who cannot approach a minister of their own community and who seek such on their own accord, provided that they manifest Catholic faith in respect to these sacraments and are properly disposed.
§5. For the cases mentioned in §§2, 3, and 4, the diocesan bishop or conference of bishops is not to issue general norms except after consultation at least with the local competent authority of the interested non-Catholic Church or community.

Guidelines for the Reception of Holy Communion (US National Conference of Catholic Bishops)

On November 14, 1996, the National Conference of Catholic Bishops approved the following guidelines on the reception of Holy Communion. The guidelines seek to remind all those who may attend Catholic liturgies of the present discipline of the Church with regard to the sharing of Eucharistic Communion.
For Catholics: As Catholics, we fully participate in the celebration of the Eucharist when we receive Holy Communion. We are encouraged to receive Communion devoutly and frequently. In order to be properly disposed to receive Communion, participants should not be conscious of grave sin and normally should have fasted for one hour. A person who is conscious of grave sin is not to receive the Body and Blood of the Lord without prior sacramental confession except for a grave reason where there is no opportunity for confession. In this case, the person is to be mindful of the obligation to make an act of perfect contrition, including the intention of confessing as soon as possible (canon 916). A frequent reception of the Sacrament of Penance is encouraged for all.
For our fellow Christians: We welcome our fellow Christians to this celebration of the Eucharist as our brothers and sisters. We pray that our common baptism and the action of the Holy Spirit in this Eucharist will draw us closer to one another and begin to dispel the sad divisions which separate us. We pray that these will lessen and finally disappear, in keeping with Christ's prayer for us "that they may all be one" (Jn. 17:21). Because Catholics believe that the celebration of the Eucharist is a sign of the reality of the oneness of faith, life, and worship, members of those churches with whom we are not yet fully united are ordinarily not admitted to Holy Communion. Eucharistic sharing in exceptional circumstances by other Christians requires permission according to the directives of the diocesan bishop and the provisions of canon law (canon 844 Section 4). Members of the Orthodox Churches, the Assyrian Church of the East, and the Polish National Catholic Church are urged to respect the discipline of their own Churches. According to Roman Catholic discipline, the Code of Canon Law does not object to the reception of Communion by Christians of these Churches (canon 844 Section 3).
For those not receiving Holy Communion: All who are not receiving Holy Communion are encouraged to express in their hearts a prayerful desire for unity with the Lord Jesus and with one another.
For non-Christians: We also welcome to this celebration those who do not share our faith in Jesus Christ. While we cannot admit them to Holy Communion, we ask them to offer their prayers for the peace and the unity of the human family.