Catholicism is a broad term for the body of the Catholic faith, its theologies and doctrines, its liturgical, ethical, spiritual, and behavioral characteristics, as well as a religious people as a whole.

For many the term usually refers to Christians and churches, western and eastern, in full communion with the Holy See, known alternatively as the Catholic Church or as the Roman Catholic Church. However, many others use the term to refer to other churches with historical continuity from the first millennium.

In the sense of indicating historical continuity of faith and practice, the term "catholicism" is at times employed to mark a contrast to Protestantism, which tends to look solely to the Bible as interpreted on the principles of the 16th-century Protestant Reformation as its ultimate standard. It was thus used by the Oxford Movement.

According to Richard McBrien, Catholicism is distinguished from other forms of Christianity in its particular understanding and commitment to tradition, the sacraments, the mediation between God, communion, and the See of Rome. According to Orthodox leaders like Bishop Kallistos Ware, the Orthodox Church has these things as well, though the primacy of the See of Rome is only honorific, showing non-jurisdictional respect for the Bishop of Rome as the "first among equals" and "Patriarch of the West". Catholicism, according to McBrien's paradigm, includes a monastic life, religious institutes, a religious appreciation of the arts, a communal understanding of sin and redemption, and missionary activity.

Frederick Antony Ravi Kumar Zacharias (born 1946) is an Indian-born, Canadian-American evangelical Christian apologist. Zacharias is the author of numerous Christian books, including Gold Medallion Book Award winner Can Man Live Without God? and bestsellers Light in the Shadow of Jihad and The Grand Weaver. He is the founder and chairman of the board of Ravi Zacharias International Ministries, host of the radio programs Let My People Think and Just Thinking, and visiting professor at Wycliffe Hall of Oxford, where he teaches apologetics and evangelism. Zacharias studied as a visiting scholar at Cambridge University and held the chair in Evangelism and Contemporary Thought at Alliance Theological Seminary from 1981 to 1984. Commentator Chuck Colson referred to Zacharias as "the great apologist of our time."

Zacharias was born in Madras, India. Zacharias claims descent from a woman (of the Nambudiri Brahmin caste) and a low caste Boatman. Missionaries spoke to one of his ancestors about Christianity and thereafter the family was converted. Zacharias grew up in a nominal Anglican household, and he himself was an atheist until the age of 17, when he unsuccessfully tried to commit suicide by swallowing poison. While in the hospital, a local Christian worker brought him a Bible and instructed his mother to read to him out of John 14. Zacharias says that it was John 14:19 that touched him and caused him to commit his life to Christ.

Christopher Eric Hitchens (13 April 1949 – 15 December 2011) was an English American author and journalist whose career spanned more than four decades. Hitchens, often referred to colloquially as "Hitch", was a columnist and literary critic for New Statesman, The Atlantic, The Nation, The Daily Mirror, The Times Literary Supplement and Vanity Fair. He was an author of twelve books and five collections of essays. As a staple of talk shows and lecture circuits, he was a prominent public intellectual, and his confrontational style of debate made him both a lauded and controversial figure.

Hitchens was known for his admiration of George Orwell, Thomas Paine and Thomas Jefferson, as well as for his excoriating critiques of various public figures including Mother Teresa, Bill Clinton, Henry Kissinger and Diana, Princess of Wales. Although he supported the Falklands War, his key split from the established political left began in 1989 after what he called the "tepid reaction" of the Western left to the Rushdie Affair. The September 11 attacks strengthened his internationalist embrace of an interventionist foreign policy, and his vociferous criticism of what he called "fascism with an Islamic face." His numerous editorials in support of the Iraq War caused some to label him a neoconservative, although Hitchens insisted he was not "a conservative of any kind", and his friend Ian McEwan describes him as representing the anti-totalitarian left.

Clinton Richard Dawkins, FRS, FRSL (born 26 March 1941), known as Richard Dawkins, is a British ethologist, evolutionary biologist and author. He is an emeritus fellow of New College, Oxford, and was the University of Oxford's Professor for Public Understanding of Science from 1995 until 2008.

Dawkins came to prominence with his 1976 book The Selfish Gene, which popularised the gene-centered view of evolution and introduced the term meme. In 1982 he introduced an influential concept into evolutionary biology, presented in his book The Extended Phenotype, that the phenotypic effects of a gene are not necessarily limited to an organism's body, but can stretch far into the environment, including the bodies of other organisms.

Dawkins is an atheist, a vice president of the British Humanist Association, and a supporter of the Brights movement. He is well known for his criticism of creationism and intelligent design. In his 1986 book The Blind Watchmaker, he argued against the watchmaker analogy, an argument for the existence of a supernatural creator based upon the complexity of living organisms. Instead, he described evolutionary processes as analogous to a blind watchmaker. He has since written several popular science books, and makes regular television and radio appearances, predominantly discussing these topics. In his 2006 book The God Delusion, Dawkins contends that a supernatural creator almost certainly does not exist and that religious faith is a delusion—"a fixed false belief." As of January 2010 the English-language version has sold more than two million copies and had been translated into 31 languages.

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..