Reformed worship is religious devotion to God as conducted by Reformed or Calvinistic Christians, including Presbyterians. Despite considerable local and national variation, public worship in most Reformed and Presbyterian churches is governed by the Regulative principle of worship.

Huldrych Zwingli, who began his reforming work in Zurich in 1518, introduced many radical changes to worship. His Sunday service, instituted in 1519, was apparently derived from a liturgy called Prone, a late Medieval service which was sometimes held before, during, or after mass. It contained the Lord's Prayer, a Hail Mary, a sermon, a remembrance of those who had died the previous week, another Lord's Prayer and Hail Mary, the Apostles' Creed, the Decalogue, confession, and absolution.

Martin Bucer, the reformer of Strasbourg, believed that proper worship must be conducted in obedience to the Bible, and for this reason he sought to eliminate many of the dramatic ceremonies which were part of the liturgy of the church. He limited worship to preaching, almsgiving, the Eucharist, and prayer. John Oecolampadius, in Basel, believed that while the Bible did not give detailed liturgical instruction, all worship must be guided by biblical principles. For him this meant that worship should be simple and unpretentious.

John Calvin's ideas about worship were influenced Martin Bucer and William Farel during his time in Strasbourg beginning in 1538. When he came to Geneva in 1536, Farel had already begun a Zwinglian reformation. His liturgy emphasized the unworthiness of the worshiper with the Ten Commandments being sung every Sunday, a practice probably taken from Martin Bucer. The service was also very didactic, with even the prayers written with the intention to instruct. Calvin did not insist on having explicit biblical precedents for every element of worship, but looked to the early church as his model and retained whatever he considered edifying. The liturgy was entirely in the vernacular, and the people were to participate in the prayers.

Calvin's Geneva became the model for all continental Reformed worship, and by the end of the sixteenth century a fixed liturgy was being used by all Reformed churches. Dutch Reformed churches developed an order of worship in refugee churches in England and Germany which was ratified at synods in Dordrecht in 1574 and 1578. The form emphasizes self-examination between the words of institution and communion consisting of accepting the misery of one's sin, assurance of mercy, and turning away those who are unrepentant.

The 1552 Book of Common Prayer was influenced by Reformed thinking through Scottish reformer John Knox's insistence on including what became known as the black rubric, a declaration that kneeling at the Eucharist did not imply adoration. Knox also wrote a liturgy for the newly founded Church of Scotland based on John Calvin's liturgy. Knox's liturgy set a structure for worship in Scotland, though ministers could improvise. Following the Union of the Crowns in 1603, the English made several attempts to impose the Book of Common Prayer on the Scots, which they fiercely resisted.

Following their return from exile in Geneva during the reign of Queen Mary I and King Philip, English Protestants known as Puritans (who remained within the Church of England) and separatists (who separated from it) began to attempt to introduce some of the more radical reforms they had experienced in Geneva into the worship of the Church of England, and in some ways to go beyond them. They sought to rid worship of any element not specifically prescribed in the Bible, though they disagreed on the practical implications of this. They also favored liturgical decisions to be made at the lowest level possible, rather than by a regional or national authority.

In the years leading up to the Reformation, baptism was often conducted in private as a celebration of the birth of children. The rite was considered necessary for salvation, and so midwives often baptized children to avoid the risk that the child would die unbaptized. Strasbourg reformer Martin Bucer made it a part of the worship service so that parishioners could be reminded of their own baptism, which was to be the sign of their incorporation into the church. The parents of children were to bring their children to the font following the sermon, and were admonished to catechize their children, a process which was intended to begin around age ten. Catechesis was considered to be entailed in baptism itself, and weekly catechetical services were instituted for this purpose. Zwingli understood baptism to be a sign of membership in a community rather than a ritual which conferred salvation on individuals. He, or possibly Oecolampadius, can be credited with first articulating this line of thought, later called covenant theology, which became the Reformed sacramental theology. During the Reformation, Anabaptists opposed the practice of infant baptism, arguing that only those who had made a profession of faith should be administered the rite. This was based on a theology of decisional regeneration, the teaching that only those who had made a decision for Christ could be saved. Against this, the Reformed believed that justification is only by grace, rather than based on any human decision.