Protestantism is one of the major groupings within Christianity. It has been defined as "any of several church denominations denying the universal authority of the Pope and affirming the Reformation principles of justification by faith alone, the priesthood of all believers, and the primacy of the Bible as the only source of revealed truth" and, more broadly, to mean Christianity outside "of a Catholic or Eastern church". It is a movement that began in Germany in the early 16th century as a reaction against medieval Roman Catholic doctrines and practices, especially in regards to salvation, justification, and ecclesiology. The doctrines of the over 33,000 Protestant denominations vary, but most include the Ten Commandments, justification by grace through faith alone, known as Sola Gratia and Sola Fide respectively, the priesthood of all believers, and the Bible as the supreme authority in matters of faith and morals, known as Sola Scriptura, Latin for "by scripture alone".

In the 16th century, the followers of Martin Luther established the evangelical (Lutheran) churches of Germany and Scandinavia. Reformed churches in Hungary, Scotland, Switzerland and France were established by John Calvin and other reformers such as Huldrych Zwingli. In addition, John Knox established a Calvinist communion in the Church of Scotland and also the Reformed Church in Hungary. The Church of England became independent of papal authority and influenced by some Reformation principles. There were also reformation movements throughout continental Europe known as the Radical Reformation which gave rise to the Anabaptist, Moravian, and other pietistic movements.

Peter John Kreeft (born 1937) is a professor of philosophy at Boston College and The King's College. He is the author of numerous books as well as a popular writer of Christian philosophy, theology and apologetics. He also formulated, together with Ronald K. Tacelli, SJ, "Twenty Arguments for the Existence of God".

Kreeft took his A.B. at Calvin College (1959), and an M.A. at Fordham University (1961). In the same university he completed his doctoral studies in 1965. He briefly did post graduate studies at Yale University.

Kreeft has received several honors for achievements in philosophical reasoning. They include the following: Woodrow Wilson, Yale-Sterling Fellowship, Newman Alumni Scholarship, Danforth Asian Religions Fellowship, and Weathersfield Homeland Foundation Fellowship.

He joined the Philosophy faculty of the Department of Philosophy of Boston College in 1965. His intellectual reputation stems from his strengths in debating and summarizing the philosophical arguments of the major Western philosophers. He has debated several academics in issues related to God's existence. Shortly after he began teaching at Boston College he was challenged to a debate on the existence of God between himself and Paul Breines, an atheist history professor, which was attended by a majority of undergraduate students. Kreeft later used many of the arguments in this debate to create the Handbook of Christian Apologetics with then undergraduate student Ronald K. Tacelli, S.J..

Peter J. Leithart (born 1959) is an American author, minister, theologian and Senior Fellow of Theology and Literature as well as Dean of Graduate Studies at New Saint Andrews College and holds a doctorate from Cambridge University. He was selected by the Association of Reformed Institutions of Higher Education to be one of the organization's 2010-2012 Lecturers. He is the author of commentaries on the Book of Kings and the Book of Samuel, as well as a Survey of the Old Testament. Other works include books on topics such as Dante's Inferno, Shakespeare, and Jane Austen. He is also the author of a book of children's bedtime stories titled Wise Words based on the Book of Proverbs.

In June 2011, Leithart was tried by his presbytery for heresy and in October was exonerated on all charges.

Peter Leithart and his wife have ten children.