Pope Francis is to make public the conclusions of his two Synods on the family in a document eagerly awaited by 1.3 billion Roman Catholics.
It will detail the pope's views about family life, marriage, contraception and bringing up children.
Many hope it will open the way for the Church to offer communion to the divorced and civilly remarried, something conservatives have resisted.
The document is the culmination of three years' work by the Pope.
BBC's Caroline Wyatt says that what is known as an Apostolic Exhortation is a wide-ranging document of more than 200 pages entitled The Joy of Love.
The Pope sent a questionnaire to families across the world asking them about their hopes and their fears.
Then he brought bishops and cardinals together for two Synods in Rome, at which he encouraged them to debate and even to disagree over issues that divide the Church in many countries.
Among the most divisive issues are offering communion to the divorced and remarried, contraception and the treatment of gay Catholics.
Our correspondent says the lengthy document will show exactly where Pope Francis stands - with some already describing it as a papal bombshell - as he steps into the minefield of Catholic teaching on the family.
While conservatives do not want him to change doctrine, liberals hope he will tell the Church to show a more merciful attitude to those whose families do not conform to the current Catholic ideal.
Some in the Church have called for measures which allow a priest or a bishop to decide privately, on a case-by-case basis, if a Catholic who has divorced and remarried can be fully readmitted and receive communion.
While progressives such as the influential Cardinal Walter Kasper of Germany support this policy, conservatives maintain it would devalue the principle established by Jesus of marriage being indissoluble.
At the conclusion of the Synod last year, Francis castigated Church leaders who, he said, buried their heads in the sand over the issue. He argued that their adherence to rigid doctrine was over-riding their concern for the suffering of families.
The papal document is also expected to call for better marriage preparation while repeating the Synod's view that homosexual unions cannot be on a par with heterosexual marriage.