Tres Dias traces its ancestry through Cursillo, which had its beginnings amid the turmoil and destruction of civil warfare and of the Second World War, which left Spain with empty churches and a sense of aimlessness and diminished dreams. Late in the 1940's, a sense of revival was stirring within the Roman Catholic Church. Small groups of friends in various Catholic action groups began to share their faith regularly to help one another. Pilgrimages were organized whereby men and women could rededicate their lives toward Christian ideals. Bishop Juan Hervas, who was active in action groups and renewal activities with the men on the island of Majorca, and Eduardo Bonin, who was involved with organizing pilgrimages, met through these sharing groups. They began to see how the church could benefit and the lives of people could be changed through studying and sharing their lives in Christ.
With a broadening vision of what these small sharing groups (reunion groups) could accomplish, weekly meetings produced periodic retreats where the reality of living a Christian life was intensely taught and experienced through support by reunion groups. These retreats became known as Cursillo de Christiandad, which means "short course in Christianity."
The Cursillo movement was confined to Spanish speaking countries until the late 1950's when a group of men from the Spanish Air Force, who were in training in Texas, and were in a Reunion Group, conducted the first Cursillo in the United States. Among the Spanish-speaking people the movement began to spread across the United States. The first English speaking Cursillo was held in the early 1960's.
Protestants who attended the weekends, saw the need to make the experience available to other Protestants. Various denominations developed their own renewal programs modeled after the Roman Catholic Cursillo de Christiandad. For various reasons (see the history of Tri-State Tres Dias, below, for an example) a need for an ecumenical protestant three-day renewal experience was felt. This led to the development of the interdenominational Tres Dias.