Restorationism, also known as Christian primitivism, is a religious perspective holding that the early beliefs and practices of the followers of Jesus were either lost or adulterated after his death, and therefore required restoration. It is a view that often "seeks to correct faults or deficiencies, in other branches of Christianity, by appealing to the primitive church as normative model".

Efforts to restore an earlier, purer form of Christianity are frequently a response to denominationalism. As Rubel Shelly put it, "the motive behind all restoration movements is to tear down the walls of separation by a return to the practice of the original, essential and universal features of the Christian religion." Different groups have attempted to implement the restorationist vision in various ways; for instance, some have focused on the structure and practice of the church, others on the ethical life of the church, and still others on the direct experience of the Holy Spirit in the life of the believer. The relative importance assigned to the restoration ideal, and the extent to which the full restoration of the early church is believed to have been achieved, also varies among groups.

More narrowly, the term "Restorationism" is used to describe a number of unrelated movements that arose during the Great Awakenings, such as the Christadelphians (from the Greek for "Brothers of Christ"), Swedenborgians (also known as, The New Church), Irvingians (the largest of which is the New Apostolic Church), The Church of Jesus Christ of Latter-day Saints (also known as Mormonism), Jehovah's Witnesses (from the tetragrammaton for God), La Luz del Mundo (Spanish for "the Light of the World"), and Iglesia ni Cristo (Tagalog for "Church of Christ"). In this sense, Restorationism has been regarded as one of the six taxonomic groupings of Christianity: the Church of the East, Oriental Orthodoxy, Eastern Orthodoxy, Roman Catholicism, Protestantism, and Restorationism. These Restorationist groups share a belief that historic Christianity lost the true faith during the Great Apostasy and that the Church needed to be restored.

The term has been used in reference to the Stone–Campbell Movement in the United States, and has also been used by more recent groups describing their goal to re-establish Christianity in its original form, such as some anti-denominational Charismatic Restorationists, which arose in the 1970s in the United Kingdom and elsewhere.

The terms restorationism, restorationist and restoration are used in several senses within Christianity. "Restorationism" in the sense of "Christian primitivism" refers to the attempt to correct perceived shortcomings of the current church by using the primitive church as a model to reconstruct early Christianity, and has also been described as "practicing church the way it is perceived to have been done in the New Testament".

Restorationism is called "apostolic" as representing the form of Christianity that the Twelve Apostles followed. These themes arise early in church history, first appearing in the works of Iranaeus, and appeared in some movements during the Middle Ages. It was expressed to varying degrees in the theology of the Protestant Reformation, and Protestantism has been described as "a form of Christian restorationism, though some of its forms – for example the Churches of Christ – are more restorationist than others".

A number of historical movements within Christianity may be described as "restoration movements", including the Glasites in Scotland and England, the independent church led by James Haldane and Robert Haldane in Scotland, the American Restoration Movement, the Landmarkists and the Mormons. A variety of more contemporary movements have also been described as "restorationist". Restorationism has been described as a basic component of some Pentecostal movements such as the Assemblies of God. The terms "Restorationism movement" and "Restorationist movement" have also been applied to the British New Church Movement.

Capitalized, the term is also used as a synonym for the American Restoration Movement. The term "restorationism" can also include the belief that the Jewish people must be restored to the promised land in fulfillment of biblical prophecy before the Second Coming of Christ. Christian restorationism is generally used to describe the 19th century movement based on this belief, though the term Christian Zionism is more commonly used to describe later forms.