Folk Catholicism can be broadly described as various ethnic expressions and practices of Catholicism intermingled with aspects of folk religion. Practices have varied from place to place and may at times contradict the official doctrines and practices of the Catholic Church.

Some forms of folk Catholic practices are based on syncretism with non-Christian or otherwise non-Catholic beliefs or religions. Some of these folk Catholic forms have come to be identified as separate religions, as is the case with Caribbean and Brazilian syncretism between Catholicism and West African religions, which include Haitian Vodou, Cuban Santería, and Brazilian Candomblé. Other syncretized forms, such as the syncretism between Catholic practice and indigenous American belief systems common in Maya communities of Guatemala and Quechua communities of Peru, are typically not described by their practitioners or by outsiders as separate religions; their practitioners generally consider themselves Roman Catholic in both name and practice.

Still other folk Catholic practices are local elaborations of Catholic custom that the Roman Catholic Church does not deem contradictory to Roman Catholic doctrine and practice. Examples include compadrazgo in modern Iberia, Latin America, and the Philippines, which developed from standard medieval European Catholic practices that fell out of favor in Europe after the seventeenth century; the veneration of some local saints, and pilgrimages in medieval and modern Europe.

Folk Catholic practices occur where Catholicism is a major religion, not only in the oft-cited cases of Latin America and the West Indies. Folk accommodations between Catholicism and local beliefs can be found in Gaelic Scotland, Ireland, Spain, Portugal, France, Italy, Poland, Germany, Austria, the Philippines, and southern India.^{[citation needed]}

In Ireland, openly Catholic worship was banned due to the Penal Laws. This led to storytellers inventing their own tales to teach the Gospel or add further lessons. These further lessons however often ended up contradicting the teaching of the Catholic Church. Within these stories a variety of recurring characters and themes appear such as the Virgin Mary, priests, Paul the Apostle, Satan, and Jesus himself.

In the Philippines, the custom of Simbang Gabi developed from the farming community. Simbang Gabi is a devotional nine-day series of Masses leading up to Christmas. On the last day of the Simbang Gabi, which is Christmas Eve, the service is instead called Misa de Gallo (Spanish for 'Rooster's Mass'). It has an important role in Philippine culture. It has its origins in the early days of Spanish rule over the Philippines as a practical compromise for farmers, who began work before sunrise to avoid the noonday heat out in the fields. Despite being exhausted by a long day's labor, the people would still attend the customary evening novenas. In 1669, the priests began to say Mass in the early mornings instead of the evening novenas more common in the rest of the Hispanic world. This cherished Christmas custom eventually became a distinct feature of Philippine culture and became a symbol of sharing.

The Catholic Church takes a pragmatic and patient stance towards folk Catholicism. For example, it may permit pilgrimages to the site of reported apparitions (e.g. Međugorje) without endorsing or condemning belief in the reported apparitions and will often declare Marian apparitions and similar miracles "worthy of belief" (e.g. Our Lady of Fatima) or will confirm the cult of local saints without actually endorsing or recommending belief. When the Catholic Church considers that there is a blatant heresy occurring, it actively rejects it and tells Catholics to stay away from such practices. This is the case of the cult of Santa Muerte (Saint Death, a personification and veneration of death). The Church has condemned the cult as blasphemous, calling it a "degeneration of religion".

One of the biggest and well-known folk religions is Vodou. It first appeared in Haiti in the 17th century, and has grown to a large religion which has over 60 million worshippers globally. It began in tribal regions of the Dahomey Kingdom which is near present-day Nigeria. Vodu is from the Fon language of Dahomey and means "god" or "spirit". Vodu and was the religion for many people in this part of West Africa. It is also the origination of the rhythmic drum beating which became a big part of worship and lwa.